I

(töV*(^4 foc 3 » S"

•* *. :. 'L .'.

í. . f

wSS*^

366

USES OF AIRPHOTOS FOR

RURAL AND URBAN PLANNING

^«sas,.

itf.! £>;.%:::*;

*^ ',-. „^

^1

I- •- ^i

vi^

-«««»?

"."_ - ..-Isïnrk«

Ai

RICULTURE HANDBOOK NO. 315 U.S. DEPARTMENT OF AGRICULTURE ECONOMIC RESEARCH SERVICE
PREFACE

Rural and urban planning for the best use of natural resources is

increasingly innportant in this country. Airphotos are a valuable tool for

planners; they can be used in many ways, such as in preparing land-use

maps, measuring the size of a lake or a field, selecting a school site, inventorying recreation facilities, and determining change in rate of land use.

Using airphotos can save time and money, and improve accuracy of studies

on which plans are based. This handbook describes how airphotos are made,

and how two disciplines based on airphoto use--photogrammetry and photo

interpretation--aid in preparing plans for rural and urban development.

The sources of all illustrations in the handbook are in appendix table 7.

The author received help from many people during the preparation of

this handbook. Information about the availability of aerial photography was

supplied by William J. Dale and Louis R. Custidero, U.S. Geological Survey;

Howard D. Wolfe, U.S. Coast and Geodetic Survey; Charles E. Taylor, National

Archives and Records Service; and in the Department of Agriculture,

Mrs. Thelma P. Link, Agricultural Stabilization and Conservation Service;

Bowman Porter, Forest Service, and Ralph M. Hooper, Soil Conservation

Service. K. P. Harris, Agricultural Stabilization and Conservation Service;

Ivan Hanson and William J, Donovan, Economic Research Service; Alan Lord,

University of Pennsylvania; and E. B. Peterson, American Institute of

Planners, provided background information*

For sale by the Superintendent of Documents, U.S. Government Printing Office

Washington, D.C., 20402 - Price 30 cents
CONTENTS

Summary ,

Introduction

Page

IV

Definitions j

Applications of airphotos 2

Use of airphotos can save time and money, and improve accuracy. 3

Start with the most economical materials 3

Types of airphotos in general use 4

Photo angles 4

Film types 5

Fornnat 5

Print types ¿

Airphoto scales . ¿

Photo types 10

Uses of airphotos in planning 12

Interpretation 12

Mapping 26

Measurement 27

Information and education 27

Photo-interpretation problems in planning 28

Pattern 28

Shape and size 28

29

29

29

Texture

Tone

Size and scale

Special knowledge 30

Steps in use of airphotos for interpretation 31

Availability of airphotos 32

How to obtain aerial photography 33

Fromi U.S. Department of Agriculture 33

From U.S. Department of Commerce 34

From U.S. Department of the Interior 34

Ordering new photography 34

Selected references 3^

Appendix figures 37

Appendix tables 38

June 1966
Summary

Airphotos have almost unlimited uses

for both rural and urban planning. Two

major uses of aerial photography are photogrammetry (for making reliable distance,

size, and height measurennents) and photo

interpretation (for identifying objects and

judging their significance).

Typical applications of these techniques

in planning include preparing base maps,

helping delineate areas where soil is unsuitable for intensive development, measuring the acreage of a lake surface, selecting a school site, determining the rate of

change from rural to urban land uses,

making a count of the total number of

parked or moving automobiles in a city

business area at one particular moment,

and illustrating planning reports. Actually,

the use of airphotos in planning is limited

only by the training, imagination, and ingenuity of planners themselves.

There is great variety in the types of

aerial photographs in general use. Airphotos nnay be vertical or oblique; they

may be in black and white or in color.

Airphotos may be square or rectangular;

and they may show a small area in great

detail or a large area in limited detail.

Both natural and manmade features can

be identified and measured on airphotos.

The level of detail discernible varies with

and depends on the quality and the scale of

the airphoto. On a small-scale airphoto or

mosaic, suchas 1:250,000, one can identify

general land forms and drainage patterns,

and distinguish between urban and rural

areas. On airphotos having a scale of

1:20,000, natural features such as hills,

valleys, and streanns, and detailed land

uses such as orchards, schools, gasoline

stations, and swimming pools can be readily

identified. At a scale of 1:4,800, the dimensions of buildings can easily be measured.

For connpilation of accurate base nnaps

and airphoto mosaics, high-quality airphotos, expensive equipment, and highly

skilled technicians are needed. For most

other uses of airphotos--such as bringing

a land-use nnap up to date, measuring the

size of a field, or choosing possible sites

for a recreation area--good airphotos are

needed, but only inexpensive equipment is

necessary. The variety in the background,

knowledge, and training of staff members of

a planning office will often be sufficient

for them to make the needed photo interpretation and measurennents. However, if

the experience of staff people acting as

photo interpreters is not directly related to

the study topic, it would be advisable to

have the interpretation done by a specialist.

False interpretation may be far more

costly than hiring consultants or letting a

contract for the work.

Airphotos are available at reasonable cost

from many Federal, State, and local

agencies, and fronn commercial firms. The

use of airphotos for only one study can

often save enough tinne to justify the cost of

the photography. In addition, even a single

set of airphotos of suitable scale can be

used for nnany purposes, thus reducing the

cost per use still further.

If existing photography is not suitable,

then a contract would have to be written

for a commercial aerial photographic firm

for new photography. Before ordering, it

is helpful to compile a list of all uses the

aerial photography is likely to serve and to

group these uses according to both priority

of need and probable time of use. Consideration must be given to the types of

qualitative data needed from the airphotos,

and to the kinds of measurennent and levels

of accuracy that will be needed, whether

such measurements are to be made from

the airphotos thennselves, fromi maps to be

prepared by photogrannmetric methods, or

from airphoto mosaics.

If several agencies in one geographic

area can use airphotos of the same type

and scale, a joint contract for flying the

photography can save each agency money.

Even if airphotos of different areas or

different scales are needed, grouping the

orders may reduce the cost. In addition,

coordinating requirements for airphotos

would prevent needless and costly overlaps

in orders, leading to further savings.

IV
Uses of Airphotos

for Rural and Urban Planning

by

Jeanne M. Davis, Urban Planner

Natural Resource Economics Division

Economic Research Service

Introduction

Airphotos are an excellent and versatile

tool for both rural and urban planning. Used

properly, airphotos can help planners save

both time and money, improve the accuracy

of their work, and help them explain to the

public the problems of change and the benefits of good planning for rural counties,

small towns, cities, and metropolitan areas.

Airphotos can be used for any of a number

of single and interrelated purposes. These

might be preparing a new base map, delineating watersheds, identifying present land

uses, determining the rate of land-use

change, inventorying recreation facilities,

helping to delineate areas where soil is

unsuitable for intensive development, bringing obsolete maps up to date, determining

extent of flood damage, estimating utilities

and services needed in a developing area,

making traffic and parking surveys, inventorying slum buildings, selecting sites for

new parks and firehouses, preparing general plans such as those for neighborhoods,

preparing precise plans such as those for

sewers and streets, or illustrating planning

reports. The remarkable versatility of airphotos as a planning tool needs nnore

widespread recognition.

This handbook describes ways in which

airphotos are useful to planners; it also

provides information about existing airphotos and ways to order both available

and new photography.

tinually being improved, and additional uses

for them continue to be found.

Photogrammetry and photo interpretation

are major uses of airphotos. Both can be

very helpful to planners.

Photogrammetry

Photogrammetry is defined in The Manual

of Photographic Interpretation (2, p, 851)

as "the science or art of obtaining reliable

measurements by means of photography."

Maps and charts, which are important tools

for planning, are made or brought up to

date accurately and quickly, and (compared

with conventional ground survey techniques)

relatively inexpensively by photogrammetric methods. Another use of photogrammetry that is of increasing importance

to planners is the securing of quantitative

land-use data directly from airphotos.

Photo Interpretation

The term "photo interpretation" has been

defined inmany different ways. The simplest

and clearest definition is: "The act of

examining photographic images for the purpose of identifying objects and judging their

significance" (2^, p. 852). Photo interpretation involves step-by-step methodical procedures which are briefly described on

pages 31 and 32 in this report.

DEFINITIONS

Airphotos

Airphotos are any photographs taken fronn

the air. The quality of airphotos is conMosaics

A mosaic is "an assemblage of overlapping aerial photographs whose edges have

Underscored numbers in parentheses refer to the

Selected References, p. 24.

1
been matched to form a continuous photographic representation of a portion of the

earth's surface" (Z),

There are three types of mosaics: uncontrolled, semicontroUed, and controlled.

Uncontrolled mosaics are compiled so

that most innage details of the individual

airphotos match. These mosaics usually

contain errors in both position and scale;

reliable measurements cannot be made

from them. The relationship of the innage

of one object to another on the airphoto

may be somewhat different than the true

geographical relationships of the objects,

and both distances and size of images may

be distorted.

SemicontroUed mosaics are constructed

so that innage details miatch, and errors

in position and scale are distributed systennatically over the entire mosaic. These

errors are not great and therefore are

difficult to perceive. SemicontroUed

mosaics are adequate for general land-use

and other studies, but they should not be

used for mapping or for other work requiring accurate mieasurements.

Controlled nnosaics are compiled from

airphotos rectified to eliminate distortions

caused by tilt; they are constructed so that

image details are well matched, and position and scale errors do not exceed specified limits. Within these limiits, precise

measurements can be made from controlled

mosaics.

Since 1958, the Soil Conservation Service

(SCS) of the U.S. Department of Agriculture

has been using controlled aerial photomosaics as the background or nnap base on

which soil boundaries and symbols are

printed in red and certain cultural features

(such as roads, houses, and schools) are

printed in black. Most of these soil maps

are at a scale of 1:20,000. The mosaics,

of course, provide details of natural and

cultural features that are not shown on

ordinary line maps, yet the photomosaic

soil maps are less expensive to prepare.

A portion of a photomosaic soil map is

shown in figure 3.^

Photo-Index Sheets

Photo-index sheets are a type of uncontrolled nnosaic. Most index sheets are compiled so that the upper right corner of each

photo (which indicates the area identification

^ The airphotos used by SCS as field worksheets

are generally at a scale of 1:15,840 (1" = 1,320*). All

airphotos in the report are grouped starting on p. 13.

symbol, the roll number, and the print

number) is shown. A portion of a photo-index

sheet is shown in figure 7. Access to an

index sheet of available photography is

helpful if one wishes to select and order

prints of a number of airphotos. After the

prints are received, the photo-index sheet

provides a working index to this collection

of airphotos. If prints of available photography are ordered, and a photo-index sheet

for this photography is not available, it is

desirable and easy to prepare an index.-^

Index sheets are very inexpensive and

generally cost less than prints of comparable scale of other mosaics. They are

quite useful for obtaining information about

land use, but should not be used for measurement.

APPLICATIONS OF AIRPHOTOS

Included among the many applications of

airphotos for planning are the following:

a. The airphoto itself may be used as a

type of nnap.^

b. The airphoto, with identifying marks

and annotations shown on the photo

itself or on an overlay, may be used

as a map base.

c. A number of overlapping airphotos

nnay be connected to formi an airphoto mosaic (figs. 7 and 14).

d. One or more airphotos may be used

as information and education devices.

Photogrammetry has two basic types of

uses for planning: Measurement and mapmaking.

Planners can use relatively simple photogranametric nnethods to ascertain data such

as the length and slope of shoreline at sites

considered for a waterfront park, the nunaber of square feet (and the approximate

number of parking places) in center city

^ To prepare an index, lay the prints out in order

by flight line on a large piece of cork or wallboard.

Place the prints in approximately correct positions

(so that roads are a continuous line rather than a

broken line, for example), and in such fashion that the

identification symbols on each print can be seen.

Fasten the prints with small pins or staples. Photograph this crude mosaic, using fine-grain film and a

camera producing the largest possible format. Have

enlargements made from the negative so that an individual print in the index is large enough for images of

large buildings, streets, and so forth, to be distinguished (as in fig. 7).

"^ A map should show scale and directional orientation; an airphoto is not constant in scale.
parking garages, the total unused acreage

(and estimated number of burial plots) in

all cemeteries in a region, and the heights

of trees and buildings in airport approach

and takeoff patterns.

Planners make extensive use of topographic or planimetric nnaps, many of which

were compiled or brought up-to-date by

photogrammetric methods. In topographic

maps, the ennphasis is on depicting land

forms (i.e., changing land elevations), while

plan^nnetric maps accent the land-use detail.

New maps prepared for special purposes,

such as topographic maps of routes for

extension of water and sewer pipelines and

large-scale planimetric nnaps of central

business districts, often can be nnade more

quickly and cheaply using photogrannmetry

rather than land-survey miethods.

Some planners have found aerial photo

interpretation a very helpful technique for

such diverse purposes as traffic surveys,

inventories of outdoor re creation facilities,

and estinnates of the rate of change from

rural to urban land uses. A frequent use of

airphotos and photo interpretation is checking the accuracy of maps, which often are

out of date.

Photo-index sheets, mosaics, and airphotos are useful both in the office and in

the field. In the office, they are an excellent

means of becoming familiar with the general

area, and are very useful for study of a

relatively small area before fieldwork is

commenced. In the field, they are used first

for orientation, and then to verify land uses,

delineate and code land uses, note changes in

land use since the photography was flown,

and so forth.

USE OF AIRPHOTOS CAN SAVE

TIME AND MONEY, AND

IMPROVE ACCURACY

The use of airphotos and airphoto techniques for many aspects of planning studies

for both rural and urban areas saves tinne,

costs less than alternative miethods, and

makes greater accuracy possible. For example, use of airphotos for mapping can,

for nnany areas, save 75 percent or more

of the time needed if only ground-survey

techniques were used. The cost of having

new airphotos made for this purpose is

more than offset by the overall savings.

SOS estimates that field use of airphotos

for soil surveys for farnn and ranch planning,

watershed planning, and the like, provides a

tremendous saving in time and cost as well

as great improvennent in the degree of

accuracy. The use of airphoto mosaics

rather than planimetric or topographic

nnaps as bases for the soil nnaps included

with soil survey publications provides additional savings in both time and direct costs,

and in addition makes possible greater precision in soil mapping, Stereopairs of airphotos are also used in producing topographic maps with small contour intervals;

these are used to great advantage for many

engineering applications.

The Agricultural Stabilization and Conservation Service (ASCS), U.S. Department

of Agriculture, uses airphotos to check

farmers* compliance with farm programs

for which they have agreed to plant within

specified acreage allotments. The photographs are taken to the farms, fields and

crops are identified, and measurements are

made to establish new field boundaries when

necessary. The photographs are then returned to the county ASCS office, where

acreage is determined by using planimeters.

Without airphotos, ASCS could not do its

work within the time limits imposed by the

length of the growing season and program

requirennents.

The Forest Service (FS), U.S. Department

of Agriculture, uses aerial photography for

many purposes. These include topographic

mapping of forest areas, tentative selection

of sites for forest roads and bridges, forest

recreation research, and recreation area

planning. Special-purpose color airphotos

are sometimes used to assess dannage

caused by forest insects. A major use of

air photos is for forest inventory; this includes selecting the points to be samipled,

locating the points on the ground, and using

the airphotos as part of the permanent

record so that the location of the sanne

sample points can be found for remeasurement pf the trees to determine growth or

mortality. Aerial photography also is used

for preliminary evaluation of areas to be

logged. In each of these uses, aerial photography saves the Forest Service time and

money.

START WITH THE MOST ECONOMICAL

MATERIALS

Although it is desirable to use only up-todate, accurate maps or controlled nnosaics

for measurement, it is not always possible

to stretch a snnall budget enough to pay for

these. Instead, compromises nnustbemade.
It is useful to list the kinds of qualitative

information needed, the types of nneasurement that must be nnade, and .the required

level of accuracy of these measurements.

This list might make it apparent that there

is no real need for great precision in

measurement at the outset of a planning

program and, instead, that the principal

needs are to know the types of land uses in

the area, what is located where, the geographic relationships between land uses,

the intensity of land use, and the approximate acreage in various land uses. If so,

airphoto index sheets, together with planimetric or topographic maps and other available materials, would be adequate sources

of data for the initial stages of planning.

Later in the planning process, it maybe

necessary to bring the available maps up to

date. This can be done rather quickly but

somewhat crudely by transferring to the

maps details from recent airphotos or even

photo-index sheets. An alternative would be

to make an uncontrolled mosaic, using only

the center portions of contact prints (because there are fewer distortions and scale

is nnore accurate in the center) of recent

aerial photographs and assembling the

prints so that there is the least possible

amount of visible distortion (for example.

matching lines so that roads are straight,

not zigzag).

Still later in the planning process, more

accurate measurements of total acreages in

various land uses and estimates of the size

of various parcels of land may be needed.

Photo-index sheets, uncontrolled nnosaics,

contact prints, and similar materials are

too crude for such use. Scaled maps brought

up to date with little concern for precise

measurements of the added data also would

be misleading. At this stage, measurements

with the needed accuracy could be obtained

by using ratioed prints (reduced or enlarged

to a specific scale) of the latest available

photographs.

As soon as the budget warrants it, and

at least by the timie it becomes necessary

to have both up-to-date and accurate inventories, measurements, and so forth,

new aerial photography should be ordered

and a controlled mosaic should be compiled from this photography or, for greatest

accuracy, a planimetric or topographic map

should be prepared from the aerial photography by photogramnnetric methods. These

three tools are the best means of acquiring

up-to-date data quickly, accurately, smd at

costs relatively low compared with alternative sources of comparable data.

Types of Airphotos in General Use

PHOTO ANGLES

Airphotos are taken fronn either approximately vertical or oblique angles. Both have

special uses.

Vertical airphotos are taken with the

optical axis of the camera at a 90-degree

angle or as nearly vertical as practicable

to the earth's surface. Verticals are used

for photogrammetric mapping because they

contain a minimunn cmnount of scale distortion. They are also used for compiling

photomosaics and for photo interpretation

(figs. 4-6, 8-13).

Oblique airphotos are taken with the optical axis of the camera at an angle less than

90 degrees to the earth's surface. There

are two types of obliques--high and low.

The adjectives, high and low, refer to the

optical axis of the camera rather than to

the altitude from which the photo was taken.

When high obliques are taken, the camera

is pointed high enough for the photo to include the horizon. Low obliques are taken

with the camera axis pointing lower, or

nnore nearly vertical, and the horizon does

not show on the photo. High obliques are

used nnore frequently than low obliques;

therefore, the term oblique used without

the adjective usually refers to high

obliques.

Both high and low obliques are excellent

as planning information devices because the

viewer can readily see the relationship of

one image to another. Low obliques are

useful for sonne interpretation purposes, but

high obliques are of very linnitedusefulness

for interpretation because more images

are obscured (see figs. 1 and 2). Another

disadvantage of obliques is that it is extrennely difficult to use them for measurement. Because of perspective, scale within

the airphoto varies greatly; nearer objects

appear nnuch larger than nnore distant ones.

Also, images of the nearer objects are

quite distinct, but those in the distance

may blend together so that it is impossible

to differentiate one object from another.
FILM TYPES

A variety of film types are now available,

but comparatively few are in general use.

Panchromatic film (black and white) is

used most often because it is adequate for

many purposes (see figs. 1-14). A yellow

filter (sonaetimes called a minus-blue filter)

generally is used with panchromatic film

to dinninish the effects of haze. Panchromatic is the naost useful film for planners.

It is also the least expensive type of filnn.

Planners will find prints from infrared

(black and white) films revealing and very

useful for forest and other vegetation

studies, and for certain soil and water

studies (including water-cour se delineation,

soil erosion, and water pollution studies).

Infrared should not be used for other landuse studies because little or no detail in

shadows is discernible, and because differences in atmospheric humidity produce

misleading changes in greyness. Various

combinations of filters with panchromatic

and infrared films are useful for special

studies.

Use of color photography has been rather

limited. Until recently the slow film speed

(requiring full sunlight for correct exposure) and the high cost of aerial color

films virtually precluded their use except

for experiments. Now, the speed of aerial

color film is the same as that of ordinary

aerial panchromatic film; therefore, exposures of color film can be made under

the same conditions as panchromatic film.

The difficulties of handling color transparencies rather than prints, the difficulties and high cost of making color prints,

and the high cost of color film itself continue to make it impractical at present for

airphoto coverage of large areas. Planners

should, however, be aware of the advantages

of color photography, which may make it

worth the difficulties and additional expense

for special-purpose coverage of áreas of

limited size. Also, it is probable that technological changes, together with increased

use of aerial color film, will result inlower

cost of both film and prints within the next

few years.

Color reversal filnn (which after processing is a transparency like the color

slides made by amateur photographers) and

prints from color reversal film are easier

to interpret than prints from black-andwhite film, because the viewer is accustomed to seeing features in color and also

because characteristics not visible on black

and white photographs are apparent on color

photographs. Landforms, cultural features,

vegetation, variation in soil types, variation

in water depths, drainage patterns, and other

images often are recognized and studied

most easily on color photographs.

Other filnns are presently of limited usefulness to planners. However, two are useful

for special-purpose studies. Orthochromatic film (black and white) would be

useful to show underwater obstructions in

harbors, rivers, and along shorelines.

Camouflage detection film, a color reversal film, is sensitive to infrared radiation and shows differences in infrared

reflectance in false-color rather than in

black and white. For example, green vegetation appears as a reddish hue, and objects

painted green to camouflage them as vegetation appear as purple, blue, or gray.

Recently, the Forest Service has been

cooperating with a film manufacturer to

improve the infrared detection qualities of

camouflage film. The new infrared aerial

color film is being tested to determine its

potential applications for detecting differences between healthy and diseased or

insect-infested trees. It seems probable

that additional applications of this new

filnn will be found. 5

FORMAT

Most aerial canneras make photos having

a square format, usually 9 inches, although

increasing use is being made of larger

square formats. Because distortion increases toward the edges of the photo area,

it is easy and not excessively expensive to

reduce distortion by using a 9- by 9-inch

square from the center of a 12- or 18-inch

square negative. The reductionof distortion

is especially innportant for vertical airphotos used for mapping and measurement,

because distortion causes inaccuracy.

At any given scale, obliques having a

rectangular fornnat of 9 by 18 inches would

sometimes be more useful to planners than

obliques of 9 by 9, Relationships between

the rural-urban fringe and the city center,

for example, could be more readily shown

on the wider and larger fornnat.

^ Infrared color and regular color photographs

illustrate city planning problems. Sweep of Creative

Power. Jn LIFE 59 (26): 70-91, Dec. 24, 1965.
PRINT TYPES

Aerial photographs usually are printed

on photographic paper. Two thicknesses,

or weights, of paper are used: singleweight and double-weight. Single-weight

paper is thin and some kinds are easilycracked or torn. Prints on single-weight,

low-shrink paper are usually used in connpiling mosaics because it is easier to cut

than double-weight and does not buckle, but

double-weight is preferred if shrinkable

paper is used. Mosaics generally are printed

on single-weight paper. Double-weight

paper is better than single-weight for prints

that will be handled a great deal--such as

those used in fieldwork. Enlargements of

individual photos also are printed on doubleweight paper. Innprovements in plastics, and

decreasing costs, have nnade it feasible to

print aerial photographs on a polyester base.

Prints on polyester are waterproof and do

not tear easily; they are excellent for fieldwork. At present, only contact prints are

available on polyester, and their cost is

about 50 percent higher than the cost of

contact prints on double-weight paper.

Photographs nnay have a shiny or dull

surface. The fornner are called glossy

prints; the latter are matte or seminnatte

prints. Single-weight paper used for aerial

photographs may have a glossy, seminnatte,

or matte finish. Double-weight paper used

for aerial photographs usually has a matte

or sennimatte finish. Prints on most polyester bases are semimatte in appearance,

Innages on glossy prints appear sharper

than those on matte prints; this factor makes

glossies more suitable for interpretation

and for reproduction than matte prints.

Matte- or semimatte-textured prints, however, are easier to mark with ink, colored

pencil, or soft drawing pencil than are

glossies, on which only special inks and

grease pencil adhere reasonably well.

AIRPHOTO SCALES

The scale of photography is generally

expressed in one of two principal ways:

(1) as a ratio or a fractional scale, or (2) in

feet or miles per inch.

The scale of airphoto negatives generally

is expressed as a fractional scale, in which

1 inch on the airphoto is equal to a certain

number of inches on the ground. This scale

sometimes is shown as a fraction, e,g,,

1/20,000, but usually is shown as a ratio,

e.g,, 1:20,000, The scale of negatives is

determined by the lens focal length and the

altitude of the camera above ground level.

The scale of contact prints^ is sometimes

expressed as a ratio or fraction, but the

feet-per-inch scale is used nnore often. For

example, although the negative scale of a

photo is given as 1:20,000, usually the contact print scale is expressed as 1"= 1,667',

The scale of enlargennents nnade fronn airphoto negatives also is expressed in feet

per inch.

Mosaic and photo-index scales are shown

in either fractional scales or miles per

inch. Scales and their equivalents in feet

per inch, inches per mile, miiles per inch,

acres per square inch, square inches per

acre i and square nniles per square inch are

shown in appendix table 3.

If the type of film used, the altitude at

which photography is flown, and other pertinent factors remain constant, the ground

resolution or annount of detail shown in

aerial photographs usually increases with

the increase in the diameter and focal

length of the lens used. An exception to

this is the high-resolution, wide-angle lens

recently developed by several firms. Focal

lengths frequently used are 6, 8 1/4, 12,

24, and 36 inches, A 6-inch focal length

lens is often used for topographic nnapping.

An 8 1/4-inch focal length lens is used for

medium-altitude photography such as that

used for Departnnent of Agriculture landuse (1:20,000) and forest (1:15,840) studies.

Lenses having a 12-inch or longer focal

length are used for large-scale work requiring little relief distortion and displacement, such as photography of urban areas

or rural areas having variable topography.

The negative scale of the photograph, the

quality and focal length of the lens, and the

type of filnn used are the principal factors

determining the degree of enlargement

feasible from a negative. The negative scale

of the photographs should be suited to the

use for which the photography is intended,

whether it is stock bought from a firnn or

agency, or new photography flown for a

specific planning project.

With each succeeding larger scale, more

airphotos are needed to cover any given

area. Thus, if all other factors are equal,

the cost of coverage increases as the scale

increases. Using a scale that is snnaller than

is needed results in less accurate work; a

scale that is larger than necessary causes

^ Contact prints are made with the negative in

direct contact with the printing paper and are the

same size as the negative, usually 9 inches square.
unjustified expense and also additional work

in using the extra airphotos.

Airphoto negative scales used for city

planning range from about 1:1,200 to 1:4,800

(1" = 100' to 1" = 400«) for studies in which

detail is needed. Scales of 1:7,920 to 1:20,000

(1" = 660' to 1" = 1,667') usually are adequate for mamy larger area land-use studies.

And scales of 1:36,000 (1" = 3,000'),

1:63,360 (1" = 1 mile), or even smaller

scales are preferable for mapping and are

also quite useful for many types of county,

regional, or State planning studies. More

infornnation about the scales useful to

planners, the purposes for which these

scales are suitable, and the type of detail

discernible at the various scales is shown

in table 1.

Table 1.--Approximate airphoto scale ranges useful for planning and

planning-relate'd studies

Sc.ale 1: 250,000

Example of uses^ Level of detail discernible ^

Studies of land forms

Studies of gross land use

Natural features:

Mountain ranges

Valleys

Lakes

Rivers

Urban areas.

Rural areas:

Forests

Farmiland

Scale 1:96,000-1:126,720

Studies of land forms Includes all discernible at preceding

Studies of gross land use scale

Urban areas:

Subdivisions

Rural areas:

Villages

Reservoirs

Transportation and connmunication:

Airports

Railroad yards

Expressways and interchanges

Scale 1:62,500-1:70,000

General land-use studies at State Detail discernible at preceding scale.

and regional levels Natural features:

Studies of watershed drainage Strealiis Flood plains

patterns Ponds Beaches

Studies of road and street patterns. Potholes Rapids

Studies of rate of rural to urban land Swannps

use change Urban land uses:

Preliminary site selection studies Residential areas

for new towns Industrial areas

See footnotes at end of table.
Table 1.--Approximate airphoto scale ranges useful for planning and

planning-related studies--continued

Scale 1:62,500-1:70,000

Example of uses-^ Level of detail discernible^

Selection of possible sites for State Urban land uses (continued):

or county parks

Preliminary site selection studies

Commercial areas

Parks and recreation areas

for new highways Race tracks

Rural land uses:

Woodlots

Cultivated fields

Pasture or idle land

Industrial complexes

Transportation and communication:

High-voltage electric transmission

towers

Pipelines

Gas and oil storage tank farms

Scale 1:25,000-1:50,000

Natural resources inventory Detail discernible at preceding scale.

Studies for reservoir site selection Transportation:

Study of potential water power Railroads

Highways

Docks

Shipyards

Urban land uses:

Subdivisions

Shopping centers

Mobile home parks

Central business districts

Drive-in theaters

Stadiums

Golf courses

Rural land uses:

Farms

Nurseries

Greenhouses

Cenneteries

Scale 1:12,000-1:20,000

Detailed land-use studies

Mapping the distribution of one crop

Housing market analyses

Shopping center location studies

Studies for selection of dam sites

School site selection

Farm land-use planning

Erosion control studies

Detail discernible at preceding scale.

Urban land uses:

Residential

Houses--single, duplex, row

Apartment buildings

Institutional

Hospitals

Churches

See footnotes at end of table.
Table 1.--Approximate airphoto scale ranges useful for planning and

planning-related studies--continued

Scale 1:12,000-1:20,000

Exajnple of uses-*- Level of detail discernible^

Soil mapping

Forest classification

Forest inventory

Community facilities

Schools

Commercial

Shopping areas

Gasoline stations

Industrial

Factories

Warehouses

Vacant land

Rural land uses:

Nonfarm residential

Farmsteads

Houses

Barns

Cropland

Row crops

Close-grown crops

Pasture

Orchards

Vineyards

Idle land

Irrigation and drainage ditches

Natural features:

Rivers

Sandbars

Streams

Ponds

Swamps, marshes

Transportation and communication:

Roundhouses

Lanes

Streets

Parking lots

Bridges

Airports

Runways

Hangars

Administration buildings

Control towers

Pipelines

Pumping stations

Oil storage tanks

Gasometers

Water storage tanks

Recreation areas:

Football fields

Baseball diamonds

Campgrounds

Swimming pools

Picnic grounds

See footnotes at end of table.
Table 1.--Approximate airphoto scale ranges useful for planning and

planning-related studies--continued

Scale 1:7,920

Example of uses"^

^

Level of detail discernible^

Classification and inventory of

buildings

Count buildings

Count railroad cars on a siding

Highway route selection

Detail discernible at preceding scale

Scale 1:5,280

Measure size of buildings

Identify individual heavy industries Detail discernible at preceding scale

Scale 1:2,400

Measure size of railroad cars and

automobiles Detail discernible at preceding scale

""" Infornnation concerning the uses of various scales is based on interviews

and on the author's own use of airphotos.

2 Some airphoto interpreters claim that greater detail is discernible in

each category; others believe less is discernible. The level of detail shown

in each group is that which the author has been able to identify. The images

were checked on single airphotos or airphoto mosaics. Viewing stereopairs

through a folding stereoscope should enable anyone who is famiiliar with the

size, shape, texture, tone, and pattern of any of these images to identify them

at the indicated scales.

PHOTO TYPES

There are several ways in which aerial

photographs are taken: (1) as single, or

individual, photographs, with a different

area shown on each photograph; (2) as a

series, with portions of the same geographic

area shown on successive photographs so

that adjacent pairs of photos in the same

flight line may be viewed stereoscopically;

and (3) as continuous strips in which one

exposure of the film provides a single

picture. For illustrations and other nonstereoscopic uses the vÇ ont inuo u s-strip

photograph would be the - width of the filnn

(either 2 1/4 or 9 inches) and as muchas 500

feet long. For stereoscopic use, two simultaneous continuous exposures are made;

each is half the width of the filnn. Each type

can be taken fronn vertical or from oblique

angles. Table 2 indicates the types of aerial

photography useful for various planning and

planning-related studies.

Single photographs of places or objects of

interest may be taken from any desired

altitudes or angles by either professional or

amateur photographers. Airphotos taken as

single photos cannot be used fo.r measurement because the scale is unknown, ground

control is absent, and there are distortions

caused by tip and tilt of the camera. Single

airphotos, however, are useful for qualitative and illustrative purposes.

Aerial photographs of an area may be

taken in one or more continuous strips.

If the airphotos are to be comparable, they

should be taken from the same altitude and

with a comnnon angle of tilt, the latter being

as nearly vertical as possible. Some overlap

of area covered by one photograph with that

covered by the next photograph is needed.

Vertical photography for stereoscopic

use in photogrammetry or photo interpretation should be flown at a constant altitude

and angle. The mininnunn overlap needed

for stereoscopic coverage is 50-percent

10
Table 2.--Types of aerial photography useful for planning and

planning-related studies

Type Uses

Photo-index sheets Select airphotos needed for study

Photo-index sheets and other uncontrolled mosaics

Obtain general innpression of topography

Obtain general impression of types

of land use change by comparing

inosaics of same area made,from

photography of different years

Prelinninary site selection for parks,

schools, and so forth, from mosaics

of recent photography

Obtain general impression of types of

land use and patterns of land use

SemicontroUed mosaics Same as for photo index sheets and

other uncontrolled mosaics

Land use studies of large areas, such

as States and regions, for which

precise

needed

measurements are nqt«

Controlled mosaics Same as for semicontrolled mosaics

Inventories of natural resources

Inventories of land uses

Base for nnap connpilation

Land use studies requiring precise

measurements

Vertical airphotos Preparation of new planimetric or

topographic maps

Compilation of mosaics

Provide data for updating maps

Inventories of natural resources, land

uses, buildings, and so forth

Site selection

Land use studies

Traffic counts

As base "nnaps" for farm planning,

delineation of soil boundaries, and

so forth

Oblique airphotos Illustrate relationships between land

uses

Note: Level of detail discernible varies with quality and scale of the mosaics

and airphotos.

11
forward lap (60-percent usually is advisable) and 20- to 35-percent side lap with

adjacent strips. For stereoscopic viewing,

a print of each of two adjacent, overlapping

photographs in a strip is used. These are

called a stereoscopic pair (stereopair).

When the areas of overlap are viewed

through a stereoscope, a three-dimensional

effect is easily obtained. The stereoscope

also magnifies images so they can be studied

more readily.

Uses of Airphotos in Planning

The two principal uses of airphoto s in

planning have already been nnentioned

briefly: Photo interpretation and photogramnnetry (the latter includes both measurement and mapping). Airphotos also have

many uses as public information and education devices.

INTERPRETATION

Interpretation of airphotos is dependent

on the recognition or identification of objects shown as images on the airphotos.

Information about the steps used in airphoto interpretation is given in the following

chapter. Here, let us consider the types of

objects or features whose images can be

identified and the types of planning studies

for which photo interpretation is a useful

tool.

Identifiable Features and Objects

Both natural and mannnade features can

be identified on good aerial photographs of

appropriate scale.

Many natural features are readily recognized on airphotos. These include mountains, valleys, and plains; rivers, lakes,

streams, ponds, and swannps; natural surface cover (which includes bedrock, loose

rock, sand, and bare soil); and natural

vegetation cover.

Man-made or man-changed features

identifiable on airphotos include agricultural and other rural land uses, urban

land uses, and transportation and communications facilities. Forests and agricultural

land uses such as fields, orchards, and

farmsteads are easily recognized. Differentiating between row crops (such as corn)

and close-grown crops (such as wheat or

barley) is relatively siinple. Distinguishing pasture frona close-grown field crops

often is difficult. Naturally reseeded wooded

areas generally appear quite different fronn

those where seedlings were planted by hand.

Orchards are recognized by the shape and

height of the trees as well as bythe pattern

in which the trees are planted. Usually

there is more ground space visible between

the fruit trees in an orchard than there is

between trees grown for timber. Farmsteads, each with its house, yard, garden,

barn, and other buildings, are readily

recognized, although the individual farmstead's pattern varies by geographic region

and by type of farm.

Many other manmade features located in

rural areas can be identified on airphotos.

These include industrial complexes and isolated factories; estates; extractive industries (including oil amd gas fields, quarries,

and strip and deep mines) and other excavations (such as borrow pits); and irrigation or drainage canals, dams, and water

impoundments.

Cities and towns are easy to distinguish,

even on airphotos of quite small scales.

Gross urban land uses, such as industrial,

comnnercial, or residential areas, are easy

to identify.

Many individual features in urban or rural

areas can be readily recognized; others

can be identified only through interpretation

of significant clues. This process sometimes is called photo deduction, because

one makes conclusions about the identity of

an image by reasoning from the details that

are known.

For example, some institutions (such as

general hospitals and schools) are easily

recognized from their images, but others

cannot be identified so readily. For instance,

a photo nnight include images of two buildings similar in size, shape, and type of

location. If building A has a relatively

large parking lot, is adjacent to a highway,

and has a railroad siding, it can be deduced that building A is a factory. If

building B has an adjacent playground, and

there are no other clues to the building use,

it probably would be deduced that the building is a school. However, caution is necessary since photo deduction is more susceptible to error than photo recognition.

Building B nnight be an orphanage or a

children's convalescent honne.

12
Figure l,~Templeton, Carroll County, Iowa,

November 1961,

Figure 2.—Bowie, Prince Georges County, Md„,

October 1962.

Figure 1 demonstrates the usefulness of high obliques to illustrate the relationships between

land uses—in this case, the relation between a village and its rural hinterland. Notice also that

the grain storage bins and houses in the middle ground obscure structures behind them.

Figure 2, a low oblique, shows an area changing from rural to urban land use. Notice the

apparent difference in size between houses in the foreground and those in the background.

13
Figure 3.—Portion of a sail survey map for Lehigh Ce««ty, P», Scale 1:15,840.

This portion of a soil survey map of the Allentown-Bethlehem urbanizing area shows the

wealth of detail that may be seen when a photomosaic, rather than a blank sheet of paper, is used

as a map base. Notice the airport, the fields, the cemetery, the drive-in theatre, and the new

subdivision. On the soil maps published by &ÇS, the cultural symbols are printed in black and

the soil symbols and boimdary lines between soil types are printed in red.

14
Figure 4.—Morton, Tazewell County, UL, June 1939. Scale 1:20,000.

The patterns of land use in a small town asid the raral area adjacent to it.are clearly seen

in this vertical photo. The population of Mortem in 1940 was 2,241, The arrow on this and the

following figures indicatestheway the photo shouldbe held so that shadows fall toward the viewer.

15
Figure 5.~Morton, Tazewell County, 111., August 1957. Scale 1:20,000.

Airphotos show the great changes in land use that occurred on the fringe of Morton between

1939 and 1957. Development followed the main roads, and only one small subdivision (lower left

corner) leapfrogged beyond the built-up area. Population in Morton was 3,693 in 1950 and 5,325

in I960.

16
Figure 6,—Rock Creek Watershed, Montgomery County, Md., March 1957, Scale 1:6,000.

Many natural and manmade features are easy to recognize on this vertical airphoto of a portion of the Washington, D.C. rural-urban fringe. Annotated features are identified in text.

17
Figure 7.—Portion of a photo-index sheet for Prince Georges County, Md., October 1963. Scale 1:63,360.

Urban, rural, and transportation patterns of land use can be readily recognized at this scale.

Annotated features are discussed in text on pages 40, 42, and 45. Photo-index sheets, a type of

uncontrolled photomosaic, are used principally as an index to a collection of airphotos. The area

covered by each individual airphoto is easy to identify (see p. 31).

18
Figure 8.—Greenbelt, Prince Georges County, Md., October 1952. Scale 1:20,000.

Woods, fields, lake, recreation area, buildings, highways, and streets are identifiable at

this scale. Notice the curved clearing through the wooded area in the lower right corner.

19
Figure 9.—Greenbelt, Prince Georges County, Md., June 1957, Scale 1:20,000.

The patterns made by Greenbelt and the fields and buildings of the agricultural research

center at Beltsville show clearly on this airphoto because of the tonal contrast with the wooded

areas. The trees are darker shades of gray in this photo than they are in figures 8 and 10 because

dark green leaves reflect less light than is reflected by the yellow, light red, and light brown

leaves of autumn. Notice the change in the lower right corner from a clearing in 1952 to a parkway in 1957, Also note the new clearing in the lower left corner and the clearings for new streets

in the woods between the lake and Beltsville,

20
Figure 10.—Greenbelt, Prince Georges County, Md., October 1963. Scale 1:20,000.

The usefulness of a time series of airphotos of a developing area is shown by comparing

this airphoto with figures 8 and 9. Notice in the lower left corner that the clearing made in 1957

now contains a divided highway that will connect with the highway under consti-uction. Time has

brought other changes. Notice the new garden apartments to the left of the interchange. Compare

the development around the Greenbelt lake in figures 8, 9, and 10, Obviously, the greatest change

was between 1957 and 1963. In this airphoto the pattern of new clearings in the woods between

the lake and Beltsville indicates additional land would soon be in residential use.

21
Figure 11,—Greenbelt, Prince Georges County, Md., October 1963, Scale 1:12,000.

Figure 12,--Greenbelt, Prince Georges County, Md., Octdjer 1963. Sc«le 1:7,200.

Differences in the amount of detail discernible at various scales are easily seen by comparing figures 11 and 12 with figures 7, 10, and 13.

22
Figure 13.~Greenbelt, Prince Georges County, Md., October 1963. Scale 1:4,800.

At this scale even the relatively narrow lines marking the tennis courts (to left of baseball

diamond) are easily seen. The shopping center <A), pool (C), and school (D) are easy to identify

at this scale. A count of vehicles parked on-street and on parking lots could be made, although

tree shadows partially obscure some cars and may completely obscure others. Notice the tonal

differei«:es between the asphalt streets and concrete sidewalks and driveways.

23
Figure 14.—Greenbelt, Prince Georges County, Md., October 1963, Semicontrolled photomosaic, scale 1:15,840,

This is a portion of Sheet 8-13 of a semicontrolled photomosaic of Prince Georges County.

In constructing the mosaic only the center parts of the airphotos for this area of Prince Georges

County were used in order to lessen errors in scale. This portion of the mosaic was made from

the airphoto shown in figure 10 and the photos adjacent to it. Notice that much less of the interchanges and of Beltsville can be seen than are shown in Figure 10, because of the differences

in scale.

24
Recreation areas such as golf courses,

baseball diamonds, and tennis courts usually

are easy to recognize because they have

distinctive patterns. Conversely, recognizing the image of a park is not always possible because it may not be sufficiently different from that of a forest. In that event,

one would try photo deduction and search

for clues such as a paved access road, a

parking lot, or picnic area. Although the

presence of one or more such clues would

suggest that the area is a park, the apparent

absence of them would not necessarily be

proof the area is not a park.

Dams and impoundments are readily

recognized. Water purification plants also

are easy to recognize. Sewage disposal

plants and refuse dumps may require photo

deduction.

Many types of transportation and communication facilities can be recognized

easily. These include airports, expressways, parkways, streets, and alleys;

bridges; harbors, ccinals, and locks; highvoltage power lines; and radio and television transmitting and relay towers.

Highways, roads, and railroads often are

easy to recognize, but sometimes photo

deduction must be employed in distinguish- .

ing between a road and a railroad, A railroad, of course, has more gentle curves

than are necessary for highways and roads,

which frequently have 90-degree angle

intersections. Heliports often are difficult

to recognize because they are quite small.

Some pipelines are easily recognized

because of the difference between the soil

or vegetation covering them and that adjacent to their trenches. Other pipelines

are not recognizable; pumping stations may

be the only clues to their location.

Telephone lines and low-voltage electric

lines nnay be recognized, but distinguishing

between them usually is innpossible.

the different features shown; between town

and countryside, for example, or between

the various buildings in a neighborhood.

Specific types of p 1 ann in g-oriented

studies for which airphotos are useful include those concerning traffic counts, parking surveys, identification of present land

uses, determination of rate of Ismd-use

changes; identification of sources of air

and water pollution, inventory of recreation

and other open-space uses, estimation of

public utilities and services needed in a

developing area, inventory of real property

for tax assessment purposes, determination of extent of flood damage, erosion control studies, condemnation and renewal of

urbaji areas, determining route locations

for highways, watershed drainage surveys,

inventory of new structures not shown on tax

maps, and selection of sites for schools,

parks, and other community facilities.

What planning information caji be gained

from airphotos? As illustrations, let us

consider four of the types of studies nnentioned above.

Traffic and Parking.--Airphotos are an

accurate source of data for use in traffic

and parking surveys. This is a special use

of airphotos and usually requires a special

flight. Both the nnoving and the parked vehicles are "frozen" in time (such as at4:00

p.m. on Wednesday, September 15, 1965);

therefore, cars, buses, and trucks in sample

areas or in a central business district or

other area can be counted on the airphotos

at any time. Pedestrian counts also can be

made. An extra advantage inherent in using

airphotos for transportation surveys isthat

there is less likelihood of duplication than

there is with surface counting procedures,

and the counts nnade on the airphotos can be

verified readily.

Photo Interpretation as a Useful Tool

for Planning Studies

The physical fornn and the structure of

neighborhoods, cities, and geographic regions are easily observed because airphotos clearly show many land forms and

land uses. The form of large areas is, of

course, seen best on small-scale airphotos

or on nnosaics; therefore, these are helpful

in regional. State, metropolitan, and county

planning studies. Conversely, large-scale

airphotos are needed for study of neighborhoods. The use of airphotos also facilitates

the comprehension of relationships between

Rate of Land-Use Change,--Planners can

nnake good use of old airphotos, for they

are an excellent, and sometinnes the only,

source of accurate data on previous land

uses, Airphotos show the direction, type,

and density of development in a changing

area. The rate of urbanization of a survey

area can be determined quickly and accurately by comparing a time sequence of

airphotos. For example, see figures 4 and

5, which demonstrate this clearly. This

procedure can provide the information on

past and present rates of land-use change

that is needed as a base for reliable resource-needs projections.

25
Air and Water Pollution.--Some sources

of air and water pollution can be seen on

airphotos. Clouds of dense, black snnoke

from an apartment house, for example, show

clearly. Industrial and nnunicipal wastes

discharged into and discoloring streams or

rivers sometimes may be observed on ordinary airphotos taken on panchromatic film;

wastes discharged into streams may be seen

clearly on color or infrared airphotos.

Recreation.--Ai r p ho t o s are a useful

source of data needed to classify and inventory present park cind recreation areas.

The airphotos can also be used to classify,

inventory, and evaluate the recreation potential of undeveloped land and water resources.

MAPPINQ

As nnentioned earlier, maps of many

types are essential tools used in planning.

A base map, showing at least the area of

the jurisdiction being planned; the major

water courses; and the railroads, highways,

and streets should be prepared if one is not

already available. Airphotos are useful in

preparing new base maps or bringing old

ones up to date. They are also very useful

for preparing many other types of maps,

including resource naaps, land-use maps,

and ownership naaps.

Base Maps

If an up-to-date, accurate base map of

adequate scale is not available, a new base

map should be made. Also, if the area being

studied is one of great change--such as an

urbanizing county--it may be quicker and

less expensive to have a new base map prepared than to bring an old base map up to

date. Airphotos can be used as the primary

source, or even the only source, of data for

the preparation of base maps. Skilled photogrannmetrists use stereoscopic airphotos

and stereo-plotting nnachine s to make the

base manuscripts needed for both topographic and planimetric maps. If adequate

recent photography is available, the final

cost of new maps would be reduced by using

it. If available photography is inadequate or

not sufficiently up to date, new photography

should be nnade. The cost of the airphotos,

even if new ones are needed, is only a small

part of the total cost of mapping.

If new photography is needed, the steps

are:

1. Determine purpose for which the nnap

will be used and the type of map

needed;

2. Review the area to be photographed,

using existing map sources;

3. Determine approximate flight lines

and altitude, selecting optimal combination of available cancera types,

lens focal lengths, and film and filter

types to provide the scale and type of

photography needed;

4. Photograph;

5. Develop and print;

6. Establish ground control after analysis of developed photo strips;'^

7. Prepare nnap manuscript by photogrammetric means; and

8. Print nnap.

The nnost satisfactory results are obtained when one firnn is given the responsibility of both nnaking the photography cind preparing the maps. If base

maps are available that are somewhat

outdated but otherwise adequate, they can

be brought up to date quickly and at relatively low cost by transferring to them

data obtained from the latest available

aerial photography.

Land-Use Maps

Planning the development of any area

requires in addition to socio-economic

data, knowledge of the area's topography,

underlying physical structure, and the

natural resources. Airphotos and photogrammetric procedures are used for the

preparation of topographic naaps, such as

those made by the U.S. Geological Survey

(USGS), which show contours of the land,

water courses and their drainage systenas,

wetlands, forests, and numerous cultural

features. Airphotos, together with field

surveys, also can be used to map soils,

geologic structure, and mineral deposits.

"Ground control is the conventional ground control surveys—horizontal or vertical—that are needed

to establish scale; to determine the factors needed in

the rectification of aerial photographs; and to provide

a network of control points for mosaicking, compilation

of planimetric and topographic maps, and the orientation of stereoscopic models as may be necessary in the

various stereoplotting devices," Charles W.Koechley,

Director, Cartographic Division, SCS.

26
Meaningful plans cannot be made unless

the types of present land uses, the percentage of land covered by buildings, the

acreage in the various land uses, and the

areal distribution of these land uses are

known. The land-use map is the simplest

means of presenting these and other needed

data in useful form.

On airphotos, general land uses may be

identified, classified, measured, and delineated. The land-use data can then be transferred to a copy of the base map or to an

airphoto mosaic.

For more detailed land-use surveys, supplemental data not shown on airphotos should

be gathered through field checks. This is in

addition to the field checks that always

should be made of all images about which

there is any question concerning identification. Enlargements of airphotos are excellent for use as field worksheets. For rural

areas, enlargements of 1"= 600'; 1" = 700';

or even 1"= 800' are adequate. For cities,

towns, and villages, enlargements of

1" = 200' are better.ö

MEASUREMENT

Many kinds of nneasurements needed for

planning studies can be made'^'from controlled airphoto mosaics or fronn single air--^

photos; still others can best be made

from stereopairs of airphotos. Their relative accuracies vary, so the type of airphoto and the method of measurement will

depend on the precision needed for each

particular job.

Many mieasurements that can be made on

planimetric maps can also be made fronn

controlled mosaics. Approximate sizes and

distances can be measured on semicontrolled mosaics, but they cannot be used

for accurate measurements. For example,

only the approximate acreage in the wooded

Ö ASCS enlarges 1:20,000 negatives to a scale of

1" = 330* for areas where fields are small and to a

scale of 1" = 660' where fields are large to determine

for each individual field the acreage of land in certain

crops; FS uses contact prints at 1:15,840 for stereoscopic study to assist in the determination of timber

types, volumes, and so forth; and SCS generally uses

stereopairs at a scale of 1:15,840 for study in the office,

then uses single, alternate airphotos in the field as a

base on which to delineate data.

area. A, and the approximate length of the

dam at Greenbelt Lake can be deternnined

in figure 14.

Most airphotos are of a much larger

scale than airphoto nnosaics and therefore

are more useful for measuring smaller

features and objects. The approximate

acreage of water surface in Greenbelt Lake

can easily be measure4 on figure 10,

(scale 1:20,QOO). At^ the larger scale on

figure 13 (1:4,800), the size of the swimming pool and the shopping center can be

determined.

Viewing a stereopair of airphotos such

as that of Greenbelt (AHV-3DD-188 and

-189 shown in the photo-index, fig. 7) one

could naeasure the heights of buildings or

trees and the overhead clearance of various

highway underpasses provided some vertical standard, such as a building of known

height, is viewable on the photographs.

Various devices have heen invented to aid

in making quick, accurate measurennents

fronn airphotos. A photograph of a special

direct-reading plastic scale for measuring

lengths is shown in appendix figure 15.

Areas can be nneasured with a planimeter,

or with a dot or circle grid (appendix

figs. 15 and l6). Height can be measured

with a parallax bar or a stereoscopic

viewer utilizing a "floating dot."

INFORMATION AND EDUCATION

Airphotos are a useful tool for infornaation and education. Statistics, words,

maps, and ordinary g round-level photographs may be used to inform the inhabitants of a city that its population growth has

been accompanied by urban sprawl, but a

set of vertical airphotos of the city over

time (in 1950, 1955, I960, and 1965, for

example) gives a clear, quick idea of the

rate and expansion of urban area (figs. 4

and 5).

Oblique airphotos are especially useful

information devices. For example, an

oblique taken in 1955 of the waterfront

along the river in Detroit or along the

channel in Washington, D.O., would show

the hodge-podge of uses that was characteristic of unplanned growth. Oblique airphotos of the same areas in 1965 would

show the sharp contrasts brought about

through urban redevelopment.

27
Photo-Interpretation Problems in Planning

As mentioned earlier, some images on

airphotos are relatively simple to recognize and identify, while others are extremely difficult. The appearance of an

image can vary with the type of filnn used;

the season and time of day the photo was

made; the scale and clarity of the print; the

shape, size, pattern, texture, smd tone of

the object; and the background of the interpreter. The more significant characteristics and the problems they pose are discussed below.

PATTERN

The outline or pattern of objects shown

on the airphotos is one of the most important characteristics in photo interpretation for planning studies. Manmade objects

generally are characterized by straight

lines or smooth curves, while natural features are characterized by irregular outlines. This dichotomy of outline or pattern

facilitates image identification.

Let us consider an example. It might be

important for a planner to know whether the

image bisecting an area that appears to be a

good potential recreation site is a stream

or an unimproved, winding road. Either

might appear as a dark or a light, curved

line. If the line is irregular, the innage is

that of a natural object. If the image is

regular in outline, it is man made. Notice

in the lower left quarter of figure 6 the

dark, irregular outline of the stream, A.

Notice also that B, while similar to A in

tone, is a straight line; because it is straight,

we are sure this line is man made. Other

characteristics lead us to infer that it is a

drainage ditch. The straight lines shown at

C and D are similar in sonne respects to the

drainage ditch, B. These lines, however,

obviously are fence rows, because shadows

of the fence posts are visible on the original

airphoto.

Pattern, in addition to its usefulness in

helping one distinguish between natural and

man-made features, also enables easy identification of certain objects or groups of

objects. For example, the baseball diamond

in the upper left quarter of figure 6 and the

pond in the lower right quarter are easily

recognized because oftheirtypical patterns.

Orchards, golf courses, railroad yards,

drive-in movie theaters, residential subdivisions, industrial areas, and even towns

and cities are identified on airphotos primarily by the patterns of their component

parts.

SHAPE AND SIZE

The shape and size of objects provide

important clues for their identification.

Some objects, suchas airport landing strips,

and highway cloverleafs, easily can be

identified solely by their shape. Other objects can be identified primarily because

of their size in relation to the size of other

objects; for example, a four-lane highway in

a rural area can easily be distinguished from

a two-lane rural road although surfacing,

width of shoulders, and other features may

be sinnilar. For other objects, the clues of

both shape and size are needed.

Shadows of an object often indicate the

shape and the dimensions of an image.

This is particularly important in vertical

airphotos, where the roof of a building or

top of sonne other object may blend so well

with the background that it could not be

identified except for the shadow it casts.

Where shadow interpretation is important,

airphotos should be held so that the shadows

fall toward the viewer, as they do in figure 6.

If airphotos are held so that shadows point

away fronn the viewer, serious misinterpretations may result. For example, hills may

seem to be valleys or gravel pits may seem

to be piles of gravel.

The shadows of trees along the fence row

in figure 6 show that the trees differ in both

size and shape. The V-shaped shadow of

building E, in the lower right quarter, shows

that the building has a pitched roof; the

shadow of building F, in the right center,

shows that the building has a flat roof; and

the shadow of building G, in the upper left

quarter, indicate that the roof has an irregular shape, with the center section of the

roof being lower than that of either side.

Comparison of the sizes of the various

buildings provides clues to their possible

use. Building G, quite the largest object

shown in this airphoto, probably is either a

school or a snnall factory. The buses in the

parking lot would lead us to deduce this is a

school. Building F, larger thcin most houses

shown in the airphoto, might be a residence

but is more likely to be in commercial or

light industrial use. Judging by its size and

shape, building E appears to be either a

28
house or a small barn. The building probably

is a house; it lacks the barnyard, irregular

paths to it, and lanes to nearby fields that

probably would be evident if it were a barn.

TEXTURE

All nnaterials and, therefore, all features

and objects, have texture. In airphotos, only

rather gross textures are discernible, but

those greatly assist in the identification of

images.

Texture differences are especially useful

in distinguishing among types of vegetation.

Even a novice can distinguish between

wooded land, which has a nubby texture, and

open land, which appears smooth or finegrained (figs. 7, 8, and 9), Distinguishing

between woods and brush and between pasture and cultivated land is more difficult.

Cultivated fields often have a fine-line texture; the lines may be straight or curved.

Pasture, idle land, and marsh also have

distinctive textures. Determining the types

of crops in cultivated fields is a task for

only highly skilled photo interpreters who

have a good knowledge of the characteristics distinguishing various crops at different seasons.

Knowledge of cover characteristics of a

tract of land nnay often be useful in landuse planning. For example, if in selecting

the site for a new airport, 10 sites are

found that appear equally good, it would save

time and money to scan the newest available photo-index sheets of those areas to

determine the type of vegetative cover at

each site. In considering total costs of

developing the airport, the cost of clearing

a wooded site (less the value of any wood

sold) would necessarily have to be added to

the land cost. On the other hand, if the

wooded land was only on the periphery of a

site, the trees would be an asset because

they would absorb some of the noise today's

planes create.

Knowledge of cover characteristics also

is of importance in selecting sites for many

other special uses, such as highways, parks

and recreation areas, and schools. For

example, if other aspects of various possible school sites are comparable, selecting a site that has a bit of woodland or

marsh would provide children and teachers

with the added advantage of an easily accessible nature laboratory.

TONE

The variations in tone (in black and white

photos) or the differences in color (in color

photos) assist in image identification. In

black and white photos the tone, or shade

of gray, varies according to the amount of

light reflected from each object. In general,

light-colored objects reflect a lot of light;

this results in a white or light-gray image

on the photo. Conversely, dark objects reflect little light, thus producing a black or

dark gray innage on the photo.

Tone, then, depends upon the amount of

light reflected from an object (which varies

according to the surface texture of the

image) and the amount of this reflected

light which strikes the film in the camera

(which varies with the filters used and

with the angle of the camera to the reflected

light.) The tone of an object also may vary

due to such factors as the weather conditions at the time the photographs were taken

and the developing and printing methods

employed. In addition, tone may vary

according to the angle from which light is

reflected to the camera. For example, on

two succeeding airphotos of a lake, the

water may appear as a dense black tone on

one airphoto and as white or light gray on

the other.

Notice the variations intone ofthe wooded

areas in figures 8, 9, and 10. Each of the

three airphotos was taken at approximately

the sanne altitude on panchromatic film with

a minus-blue filter using a camera with an

8 1/4-inch focal length lens. The wooded

areas in figure 9 (airphoto taken in June)

are darker than those in figures 8 and 10

(October) because green leaves reflect less

light than yellow or red leaves reflect.

SIZE AND SCALE

For airphoto recognition, identification,

and interpretation, the size of the feature

or object photographed and the scale of the

print are to a degree linked. As an example,

very large features such as mountain ranges

can be recognized on prints of the very

snnall-scale photos taken and transmitted

from weather satellites. At nearly the other

extreme, one automobile can be distinguished from cinother in a parking lot, and

the automobiles can be counted, on a single

airphoto having a scale of 1:6,000 (1" = 500*).

29
(See fig. 6; there are buses and cars in the

parking lot.) If one uses a stereopair of airphotos and a stereoscope, vehicles can be

counted on airphotos of even smaller scales.

Ease of recognition varies with the size

of the feature or object and the scale of

photography. The lake shown in figures 7,

10, 11, and 12 is an image many people

can easily recognize as being a lake, but

notice how much easier it is to recognize

on figure 10, at a scale of 1:20,000

(1"= 1,667'), than it is on figure 7 at a

scale of 1:63,360 (1" = 1 mile). Observe,

also, that the additional increases in scale

in figures 11 and 12 over that of figure 10

add little if anything to one ' s ability to recognize the lake. On the other hand, look again

at figure 10 and notice image B. Then look

at image B on figures 11 through 13, Because the object itself is relatively snnall,

few people will be able to recognize the

image on figure 10, some will recognize it

on figure 11, and others nnay not do so until

they look at figures 12, or even 13. It is

not distinguishable at all on figure 7.

SPECIAL KNOWLEDGE

Knowledge in many disciplines is necessary for detailed, accurate interpretation

of all land uses shown in airphotos. Fortunately, a more general fund of infornnation often is adequate for identification or

interpretation of images of many objects in

which planners are most interested. When

general knowledge is inadequate, photo interpreters skilled in various specialties

should be consulted concerning specific

photo-interpretation problems.

Let us consider a few examples. Almost

anyone should recognize the image of a tree

on an airphoto of adequate scale--because

it is an object with which we are thoroughly

fanniliar, even though we are not accustonned

to seeing it fronn the air. Identifying the

species of the tree is more difficult and

requires special knowledge. Many people

might be able to identify the tree as being

of a deciduous or coniferous type; relatively

few would be able to say whether a deciduous tree is an oak rather than a maple,

because this identification depends upon

knowledge of ecology and forest types.

Most people should be able to identify a

building on an airphoto of adequate scale.

Identifying the use for which the building

was designed often depends upon special

knowledge. Many people nnight be able to

identify a gasoline station because it is a

distinctive object (or combination of objects)

with which we are fanniliar, but the same

people might have difficulty in identifying a

store, a school, or a stable because they

may not be familiar with the distinguishing

characteristics of each of these building

types. Planners, geographers, architects,

builders, and others with special knowledge

of building types could identify many buildings as being residences, hospitals, stores,

or schools.

When is a specialist's help needed? For

many planning studies, no outside help

should be needed. But for other studies,

even a large and diversified planning staff

may have inadequate skills. Both the quantity and the quality of information that can

be obtained fronn airphotos depend upon the

background of the person using them. If the

background, training, and experience of the

staff acting as photo interpreters is not

directly related to the topic of the study, it

would be advisable to have the interpretation done by somieone who is qualified in

that subject. False interpretation may be

far more costly than hiring consultants or

letting a contract for the work.

Electronic printers are among recent developments that have made it possible to

obtain better quality prints fronn airphoto

negatives than was possible with earlier

types of contact printing equipment. Similarly, research now underway will lead to

the development of sophisticated electronic

devices and techniques for automatic identification, counting, measuring, and mapping

of naany land uses. These techniques and

devices should be very useful to planners.

Forerunners of these--the Model T's ofthe

electronic age--already are in use. It is

probable that landfornns, vegetation, lakes

and streams, roads and railways, and urban

and industrial agglonnerations will soon be

identified by automated photo scanning and

comparison devices. However, it is unlikely

that machines will replace skilled photo

interpreters who can differentiate, for exannple, the uses of various buildings in an

urban area. Just as autonnated mapping procedures have helped rather than replaced

skilled cartographers, automated photo

identification procedures will provide plan-

'^ners with much useful data but will not provide all the details that can be obtained

through photo interpretation.

30
Steps in Uses of Airphotos for Interpretation

A great amount of information can be

obtained by studying photo-index sheets,

mosaics, and single airphotos with the

unaided eye or with a single magnifying

lens. More detail can be seen by studying

stereopairs of airphotos with the aid of a

lens or mirror stereoscope. For special

studies, airphotos taken with cameras using

certain kinds of film and filter combinations

may be needed to maximize the tone contrast of the objects of interest.

Areas to be studied may be selected by

methodically scanning photo-index sheets

or mosaics. For example, if one were looking for undeveloped land for a park site

near Washington, D.C.i in the WashingtonBaltimore corridor, one would scan the

index sheet or sheets of the latest available photography of that area, A portion

of one index sheet covering the area is

shown in figure 7.

When one scans figure 7 for a site for

a park having a minimum of 500 acres of

undeveloped land, it is apparent that the

only possible sites within the area shown

are at locations C, and D, and E. The

three areas to be studied would be marked

on the photo index sheet or on a transparent

overlay. If field checks of the areas showed

that residential or other development had

not occurred since the airphotos were flown,

airphotos that include the three areas would

be selected and ordered for detailed study.

A transparent piece of plastic on which

has been marked a square the size of one

airphoto at the scale of the photo-index

sheet (in this case, a square 2.8" x 2.8")

is useful in determining the area coveredby

each individual airphoto. The plastic is

held so that the upper right-hand corner of

the square coincides with the upper righthand corner of each of the airphotos on

which the area of interest appears. Airphotos AHV-3DD-187, -188,-189, and -190

would be ordered for stereoscopic study of

site C; airphotos AHV-3DD-166, -167, and

-168 would be ordered to study site D; and

airphotos AHV-3DD-191, -238, -239, and

-240 would be ordered for study of site E.

Airphotos AHV-3DD-189 and -190 would be

used to study site E as well as site C.

Inspection of a topographic map of these

possible sites may be made before the airphotos are ordered or may be made in

conjunction with interpretation of the airphotos. The boundaries marked on the

photo-index sheet should also be marked

on the airphotos and on the map.

Analysis of the selected areas would be

made by viewing the stereopairs of airphotos through a stereoscope. An inexpensive folding stereoscope designed for field

use provides adequate magnification for this

and many other types of planning studies.

a. The first step in the analysis is to look

for readily identifiable images that are

undesirable in a park site because

these would quickly eliminate the need

for further study of the area. To prevent optical illusions, airphotos should

be held so the shadows fall toward the

observer.

b. Methodical scanning of airphotos, like

methodical scanning of a book, is

quicker and more accurate than haphazard scanning.

c. All innages of interest for a particular

study should be marked and annotated

on one of each pair of airphotos. Ink,

soft colored pencils, and soft drawing

pencils can be used to nnark directly

on sennimatte airphotos; ink and

grease pencils can be used to mark

directly on glossy airphotos. This is

quicker and cheaper than marking on

nonshrink overlay materials and

offers fewer opportunities to confuse

or lose needed data. However, photos

that must be cleajied to use again

should be marked only with grease

pencil or acetone-soluble ink. When

preliminary study of the airphotos has

been made, data can be transferred to

overlays; grease pencil marks can be

wiped off the airphotos with a bit of

cotton dampened with carbon tetrachloride, and acetone-soluble ink can

be removed- with acetone-dannpened

cotton. Grease pencil and soft drawing pencil marks sometimes can be

removed with a gum eraser without

danaaging the surface of the print.

Caution; Fumes from all grease

solvents are toxic. Use these solvents

only with adequate ventilation. Some

solvents are also ñammable. Read the

label and follow carefully any precautions listed.

d. Images that are not easily recognized

should be carefully studied for clues

that may help the viewer deduce enough

additional information to identify the

image. If the image still is not identified, then one must seek still other

clues in the area adjacent to it,

synthesize all the bits of information

31
concerning the image, and make an

inference about its possible identity.

Field checks should be made to verify

the identification.

e. Delineating images to be transferred

to a map base can often be done most

easily while viewing the images

through the stereoscope. Generally, it

is preferable to mark on the righthand print of the stereopair.

f. When all images of interest have been

identified, annotated, and delineated,

transferring data to a map base will

be facilitated if the images are classified into various categories, and

images in the first category are

mapped first, images in the second

category mapped second, and so forth.

If images fromi nnore than one pair

of airphotos are to be mapped, it

may be quicker Süid easier to transfer

all the data fronn one pair of airphotos and then transfer data from a

second set of airphotos rather than

mapping, first, for example, streams

shown on all airphotos, and then

nnapping all roads. Establishing standard procedures for transferring data

will lessen chances of error. Use

of standardized classifications and

standardized mapping synnbols also is

helpful.^

Detailed information concerning the various steps in airphoto interpretation is given

in the Manual of Photographic Interpretation (2), Especially worthwhile for planners

are t"he chapters on the Fundamentals of

Photo Interpretation, Photo Interpretation

of Soils, Photo Interpretation in Agriculture, Photo Interpretation in Urbam Area

Analysis, and Photo Interpretation in Geography.

Availability of Airphotos

After a planner has determined the type

of aerial photography required, how and

where can it be ordered? Airphoto coverage

of almost all of the United States is available; the area of interest probably has been

photographed a number of times. Various

Federal and some State, county, and city

agencies, and commercial firms may have

available the types of photography needed.

If any of these are suitable, it usually is

quicker, easier, and cheaper to buy prints

of the existing coverage than to order new

photography.

The Map Information Office, U.S. Geological Survey (USGS), Washington, D.C.,

20242, publishes an index map on the Status

of Aerial Photography which indicates the

Federal or local government agencies, or

commercial firnns, holding negatives of

recent photography best for nnost uses.

The Map Information Office also publishes

a map showing the Status of Aerial Mosaics.

It indicates areas for which mosaics are

available and the agencies from which they

may be ordered.

Most of the available photographic coverage of the United States has been taken

for Federal government agencies, and of

this, the majority of the photography has

been made for the Department of Agriculture. Within the Department the greatest

coverage has been made for ASCS. Numerous areas of the United States have been

photographed for SOS. The Forest Service

has airphotos of areas where National

Forests are located.

In the Department of the Interior, the

U.S. Geological Survey has coverage of

many parts of the Nation.

The Coast and Geodetic Survey (C&GS),

Department of Commerce, has coverage of

the coastal areas and navigable rivers.

More aerial photography is available for

many areas of the United States than is

generally realized. An example of the types

of major vertical aerial photographic coverage available for one area is shown in

appendix table 4, which indicates recent

coverage of Fairfax County, Va.; data include the area covered, year photography

was flown, lens focal length, negative and

contact print scales, scales of enlargements available, suid the source of the airphotos. Similar details about mosaics are

shown in appendix table 5, Infornnation about

available photo index coverage is shown in

appendix table 6. In addition to large-area

coverage, there is a great quantity of strip

and spot vertical photography and oblique

^ For suggested land-use classifications see the

Standard Land Use Coding Manual^ prepared by the

Urban Renewal Administration, Housing and Home

Finance Agency (now the Dept, of Housing and Urban

Development), and the Bureau of Public Roads, U.S.

Dept. of Commerce, Jan. 1965. Available from the

Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402, $0.50 per copy.

32
photography flown for cities, highway de- been compiled for a planning department.

partments, land developers, builders, and

others.

Amassing data on regional. State, county,

or city coverage is tedious and time-consuming work; however, when suchdata have

it takes relatively little time and effort to

keep them current. The difficulty of compiling such information is far outweighed

by its usefulness.

How to Obtain Aerial Pliotography

The Geological Survey's index nnaps on

the Status of Aerial Photography and the

Status of Aerial Mosaics show the names

and addresses of the firms and the Federal,

State, and local agencies from which the

general-purpose photography indicated on

the maps can be ordered. Some agencies,

upon request, will provide maps or lists

indicating the specific areas their photography covers, the negative scale or contact

print scale of the photography, and the

number of graphic-index sheets or photoindex sheets (if available) that cover each

county or other area. Price lists, usually

separate from the status maps or lists,

show the scales of photo-index sheets, contact prints, and enlargements available and

give detailed instructions for ordering

photography.

Requests for these maps or lists and for

all photography should indicate the exact

area of interest, including State, county,

and map coordinates. When prints are

ordered, an accurate sketch, marked map,

or other description would help the firm or

agency select the photographs needed, if

identification symbols and roll and print

nunnbers are not known. If prints of a

number of airphotos are needed, the photoindex sheet or index map should be ordered

first to use in making the selections. Other

required data include the type and approximate scale of photos required, whether

stereoscopic coverage is needed, and

whether prints should have glossy or matte

finish. If prints at an accurate scale are

needed, state this on the order, specifying

the scale desired.

If available photography for a large area

is to be ordered, the photo-index sheets

should be checked carefully. Some contract specifications require that strips of

below-standard photographs be reflown; the

replacement photography generally is reflown at the contractor's convenience, and

may be done as much as 6 months after the

original photography was flown. The result

is unsatisfactory for some planning purposes. For example, if the original flight

for coverage of an urbanizing county was

in June and the replacennent flight was in

September, a great amount of construction

may have occurred in the rural-urban

fringe. Because of this, the data on present

land use derived from the photography would

be somewhat misleading, statistics on landuse change made by comparing this photography with an earlier set of photographs

also would be misleading, andtraffic counts

for the entire area could not be made.

FROM U.S. DEPARTMENT OF

AGRICULTURE

Maps of each State for which they have

photographic coverage are available free of

charge from ASCS, FS, and SCS. These

maps indicate the area covered, the year the

latest photographs were taken, the negative

scale of the photography, the focal length of

the lens used, and the type of film used.

Areas under contract for new photography

also are indicated. Photo-index sheets for

areas served by the local offices of ASCS,

FS, and SCS may be viewed at those offices.

Requests for the ASCS maps, requests

for information about earlier ASCS photographic coverage available, and orders for

ASCS photo index sheets and aerial photography in Eastern States should be addressed

to: 10

Eastern Laboratory

Aerial Photography Division, ASCS

U.S. Department of Agriculture

45 South French Broad Avenue

Asheville, N.C. 28801

^° Photography is held at Asheville for the following

States: Alabama, Connecticut, Delaware, Florida,

Georgia, Illinois, Indiana, Iowa, Kentucky, Maine,

Maryland, Massachusetts, Michigan, Mississippi, Missouri, New Hampshire, New Jersey, New York, North

Carolina, Ohio, Pennsylvania, Rhode Island, South

Carolina, Tennessee, Virginia, and Wisconsin. ASCS

does not have photography of Vermont; for USDA's

airphotos of Vermont, contact the Forest Service.

33
Orders for photo-index sheets and photography for Western States should be sent

to:^^

Western LaboratoryAerial Photography Division, ASCS

U.S. Department of Agriculture

2505 Parley's Way

Salt Lake City, Utah 84109

Requests for information about SCSphoto

index sheets, airphotos, mosaics, and

orders for thenn, should be addressed to:

Cartographic Unit

Soil Conservation Service

Federal Center Building

Hyattsville, Md. 20781

The Forest Service has photography ofthe

National Forests and National Grasslands;

the office in Washington, D.C,, holds negatives and index prints for its photography

in the eastern United States and for Alaska,

Airphotos for western States are available

frona the Service's regional offices. Inquiries concerning all FS photography may

be sent to:

Division of Engineering, Forest Service

U,S, Department of Agriculture

Washington, D,C. 20250

Most ASCS coverage made onnitrate film

from 1936 through 1941 has been transferred to a fireproof room at the National

Archives because this type of film is highly

flammable. All SCS photography taken before 1940, and nitrate coverage taken in

1941 and 1942 which is not shown on current

SCS aerial photography status maps, has

been transferred to the National Archives.

Information about coverage at National

Archives should be addressed to:

National Archives and Records Service

Cartographic Branch

General Services Administration

Washington, D.C. 20408

^ ^ Photography is held at Salt Lake City for the

following States: Arizona, Arkansas, California, Colorado, Hawaii, Idaho, Kansas, Louisiana, Minnesota,

Montana, Nebraska, Nevada, New Mexico, North

Dakota, Oklahoma, Oregon, South Dakota, Texas, Utah

Washington, and Wyoming, ASCS does not have photography of Alaska; FS has photos of part of the State.

FROM U.S. DEPARTMENT OF

COMMERCE

Photographic coverage held by the U.S.

Coast & Geodetic Survey is shown on ozalid

copies of index nnaps. Each nnap shows the

date of photography (nnonth, date, andyeai^),

scale of negatives, type of film, flight lines,

and photograph exposure numbers. Requests

for information, and orders for index nnaps

and airphotos, should be addressed to:

Director, Coast & Geodetic Survey

Attn.: Photogrammetry Division

Washington Science Center

Rockville, Md. 20852

FROM U.S. DEPARTMENT OF

THE INTERIOR

Maps of each State showing photographic

coverage flown for the U.S. Geological Survey are available free of charge from the

Map Information Office.

Map Information Office

U.S. Geological Survey

Washington, D.C. 20242

These maps indicate the areas covered,

the year the photography was flown, the

negative scale of the photography, the focal

length of the lens used, and the identification

code of each project. The nnaps also show

longitude and latitude, county boundaries and

nannes, and indicate outlines of topographic

quadrangle maps, each of which covers

either 15 or 7|^ minutes of longitude and

latitude.

Photo-index sheets for USGS photography

follow the sanne outlines as the quadrangle

nnaps and cover either 15 or l^ minutes

of longitude and latitude. Price lists and

other infornnation needed for ordering airphotos or photo-index sheets are also

available from USGS.

ORDERING NEW PHOTOGRAPHY

If existing airphoto coverage is not suitable, then the planner will need to contract

with a connnnercial aerial photography firm

to fly the required photography. Before

ordering, it is helpful to connpile a list of

all uses the aerial photography is intended

34
to serve and to group these uses according

to both priority of need and probable time

of use. Have a clear notion of how the

photography will fit both present needs and

the future work program.

Consider the types of qualitative data

needed and the kinds of measurement and

levels of accuracy that will be needed. Decide in advance whether a high level of accuracy is necessary. After photography is

flown for use in providing only qualitative

information, it will be too late to decide that,

on second thought, a new planimetric map

of the area is needed within the year or that

a controlled mosaic is neededinnmediately.

Why will it be too late? Because the type of

camera used, the lens focal length selected,

the altitude at which the plane is flown, the

amount of tip and tilt allowed in the negatives, the way the flight lines are laid out,

the requirennents for ground control for the

photography, and even the type of plane used

are quite different for photography made for

qualitative information than for photography

needed for mapping and accurate measurenaent. Unless the contractor knows exactly

what uses are expected to be made of the

photography, it will be innpossible to get the

maximum benefit for each dollar spent on

this very versatile tool.

Many factors determine the quality ofthe

photography and, consequently, its usefulness to the planner. For example, ifthe pilot

of the plane or helicopter is not sufficiently

skilled in ñying for the purpose of taking

aerial photographs, the airphotosmight contain distortions that would make thenn difficult or impossible to use for either nnap

or measurement purposes.

Comparatively few people know aerial

photographic equipment, films, filters, and

so forth, well enough to write the specifications for a contract without assistance. For

this reason, planners' needs will best be

met and the public interest will best be

served if the planner consults several

reputable firins concerning his specific

aerial photography needs before bids are

asked for or a contract is written.

Airphoto contract specifications prepared

by various agencies are good guidelines.

One excellent publication is the Reference

Guide Outline Specifications for Aerial

Surveys and Mapping by Photogramnnetric

Methods for Highways (S). Detailed information about technical specifications for

contracts is given in the Manual of Photogrammetry (1).

Names and addresses of reputable firms

specializing in aerial photography can be

obtained in several ways. The Map Information Office, U.S, Geological Survey, provides the nanaes and addresses of commercial firms whose photography is indicated

on the Status of Aerial Photography map.

The photo-index sheets available from

ASCS, FS, and SCS show the name and

address of the firm which made the photography. Additional infornnation about commercial aerial photography firms may be

found in advertisements in Photogramnaetric Engineering, the journal of the

American Society of Photogrammetry. State

highway departnnents nnay be very helpful

in providing information about contract

specifications and firms. Planning departnnents known to have ordered new photography should be an excellent source of

information about firms. Discussions with

persons in other planning departments also

provide the opportunity to gather, informally, opinions on the cooperativeness and

reliability of various aerial photography

firms.

Consultations with other groups that might

need airphotos for their work also offer the

possibility of coordinating two or more

orders for new photography. If several

agencies in one area can use airphotos of

the same type and same negative scale, a

joint contract for flying the photography

can save each agency money since each

would pay only a part of the total cost of

the negatives. Both might also save money

on the prints ordered, because the cost per

print usually decreases in proportion to the

nunnber of prints ordered from each negative.

Even if photography of different areas or

different scales is needed, it is desirable

for agencies to put their individual contracts together as a package for subnnission

to prospective contractors. There are

several advantages: (1) By grouping orders

for photography, the overall order is larger;

the cost per square mile for photography of

large areas often is less than the cost for

small areas, (2) Aerial photography can be

flown on relatively few days each month

(because of cloud cover, haze, rain, and so

forth) and during only a few months of the

year for certain photogrammetric or photo

35
interpretation uses, "^^ The better aerial

photography firms are busy; therefore, it

may be impossible to get one of these firms

to do the work unless the contract is large

enough to be attractive. (3) The more experienced firms are more likely to produce

airphotos of the necessary high quality and

accuracy.

Coordinating requirements for aerial

photography also prevents needless and

costly overlaps in orders. This is especially important in orders for new airphoto negatives, for photogrammetric

work to prepare new maps or update

old ones, and for compilation of airphoto

mosaics. Preventing an overlap in ordering any one of these could save thousands

of dollars.

Selected References

(1) American Society of Photogrammetry.

1952. Manual of Photogrammetry.

Ed. 3,l,200pp.,illus. Falls Church,

Va.

(2)

I960. Manual of Photographic Interpretation. 868 pp., illus. Washington, D.C. (Now located at Falls

Church, Va.)

(3) Avery, T, Eugene,

1962. Interpretation of Aerial

Photographs; An Introductory College Textbook and Self-Instruction

Manual. 193 pp., illus. Burgess

Publishing Company, Minneapolis,

Minn.

(4) , and Meyer, Merle P.

1961. Contracting for Forest Aerial

Photography in the United States.

U.S. Forest Serv. Lake States

Forest Expt. Sta. Paper 96, 37 pp.

12 For urban planning, mapping of both rural and

urban areas, and many engineering studies, itis better

to have photography flown in either early spring or late

fall because objects are not obscured by snow or by

foliage of deciduous trees. On the other hand, photography to be used for studies of agricultural land use

(such as acreage in various crops) should be flown

during the season when most crops can best be seen

(for most crops this would be summer). The photography needed for forest surveys varies with the species

of trees in the area and with the specific type of study

to be made.

(5) Branch, Melville C, Jr.

1948. Aerial Photography in Urban

Planning and Research. Harvard

City Planning Studies XIV, 149pp.,

illus. Harvard University Press,

Cannbridge, Mass.

(6) Lueder, Donald R.

1959. Aerial Photographic Interpretation; Principles and Application.

462 pp., illus. McGraw-Hill Book

Company, Inc, New York.

(7) Marschner, F. J.

1959. Land Use and Its Patterns in

the United States. U.S. Dept. Agr.

Handb, 153, 277 pp., illus.

(8) Photogrammetry for Highways Committee.

1958. Reference Guide Outline

Specifications for Aerial Surveys

and Mapping by Photogrammetric

Methods for Highways. 124 pp.,

illus. U.S. Govt. Printing Office,

Washington, D.C. 20402.

(9) Ray, R. G.

1960. Aerial Photos in Geologic Interpretation and Mapping. U.S.

Geol. Survey Prof. Paper 373,

230 pp., illus.

(10) U.S. Soil Conservation Service.

1966. Aerial-Photo Interpretation in

Classifying and Mapping Soils.

U.S. Dept. Agr. Handb. 294, illus.

(11) Whitmore, George D.

1941. Elements of Photogrammetry.

136 pp., illus. International Textbook Company, Scranton, Pa.

36
Appendix Figures

5 feet 66 feet 200 feet 396 feet

\ i i I

l«liflifflppB|f*lt«l|lll^^

i

!'^|K|pC?SE3Br ÄÄiÄÄ PPFWWAWÏÏP^PP» «líiÉnA illllIlIllllIllîîlllllîlllMW

Figure 15 -Photograph of a device used by Soil Conservation Service personnel to measure distance and acreage

on airphotos. The dots and grid lines have been printed on a piece of clear plastic. A white opaque coating around

the edge of the plastic permits printing of 4 direct-reading scales. On the front, at top. measurements from 1 to

396 feet can be read directly from airphotos having a scale of 1:7,920. The eight large squares onthe left are used

to measure acreage on photos iiaving ascaleof 1:7,920 (1" = 660'); each dot equals .10 acre andeach square equals

10 acres At 1-15,840 (1" = 1,320^ each dot equals .20 acre and each square equals 20 acres. The four squares on

the right, subdivided into four squares each, are used to measure acreage on photos having a scale of 1:5,280

(1" = 440')- each dot equals .044 acre, each small square equals 1.11 acres, and each large square equals 4.44

acres.

o o o o o

o o o o o

o o o o o

9 o o o o

o o o o o

o o o o o

o o o o o

o o o o o

o o o o o

o o o o o

o o o o

o o o o o

o o o o o

o o o o o

3 o o o o

o o o o c

3 o o o o

o o o o o

o o o o

o o o o

9 o o o o

o o o o o

3 o o o o

o o o o c

o o o o o

o o o o

o o o o o

o o o o

o o o o c

o o o o o

o o o o o

o o o o o

o o o o o

o o o o o

o o o o o

o o o o o

o o p o o

3 o o o o

o o o o o

3 o o o o

o o o o o

o o o o o

o o o o o

o o o o o

o o o o o

o o o o o

> o o o o

o o o 0.0

o o o o °

o o o o o

ol o o o o o

lo o o o

o o o o

o o o o o

o o o o o

o o o o o

o o o o o

o o o o o

3 o o o o

o o o o o

o o o o o

o o o o o

o o o o o

o o o o o

o o o o o

o o o o o

o o o o o

o o o o o

o o o o o

o o o o o

o o o o o

o o o o o

o o o o o

o o o o o

o o o o o

o o o o o

o o o o o

o o o o o

o o o o c

o o o o

o o o o o

o o o o o

o o o o o

o o o o ®

o o o o o

o o o o o

o o o o ®

o o o o o

> o o o c

9 o o o o

o o o o c

9 o o o o

o o o o o

o o o o o o o o o

o o o o o

o o o o o

o o o o o

g o o o o

o o o o o

3 o o o o

o o o o o

3 o o o o

o o o o o

o o o o o

o o o o o

o o o o o

o o o o o

o o o o o

o o o o c

o o o o o

o o o o o

o o o o|

o o o o jo

o o o o o|

o o o ® ®

o o o o o

g o o o o

o o o o c

g o o o o

o o o o o

o o o o o

o o o o o

o o o o o

o o o o o

o o o o o

o o o o o

o o o o o

o o o o o

o o o o o

o o o o o

o o o o o

3 o o o » o

o o o o C

o o o o o

, o o o c

o o o o o

o o o o o

o o o o o

o o o o c

o o o o o

o o o o o

9 o o o o

o o o o c

o o o <} o

o o o o o

o o o o o

o o o o o

o o o o c

9 o o o o

o o o o o

g o o o o

o o o o o

o o o o o

o o o o o

o o o o o

1 mile. Figure 16..-Example of an acreage calculating grid prepared by the Soil Conservation Service. Scale is 4

The original grid is printed on clear plastic. Similar circle or dot grids for various scales

can be made quite easily on any dimensionally stable plastic.

37
Appendix Tables

TABLE 3.—VERTICAL AIRPHOTO SCALES AND EQUIVALENTS

Feet Inches Miles Acres per Square inches Square miles

Scale per inch per mile per inch square inch per acre per square inch

1:500 41.667 126.720 0.008 0.0399 25.0906 0.00006

1:600 50.000 105.600 0.009 0.0574 17.4240 0.00009

1:800 66.667 79.200 0.013 0.1020 9.8010 0.00016

1:1000 83.333 63.360 0.016 0.1594 6.2726 0.00025

1:1200 100.000 52.800 0.019 0.2296 4.3560 0.00036

1:1500 125.000 42.240 0.024 0.3587 2.7878 0.00056

1:2000 166.667 31.680 0.032 0.6377 1.5682 0.00100

1:2400 200.000 26.400 0.038 0.9183 1.0890 0.00143

1:2500 208.333 25.344 0.039 0.9964 1.0036 0.00155

1:3000 250.000 21.120 0.047 1.4348 0.6970 0.00224

1:3600 300.000 17.600 0.057 2.0661 0.4840 0.00323

1:4-000 333.333 15.840 0.063 2.5508 0.3920 0.00398

1:4800 400.000 13.200 0.076 3.6731 0.2723 0.00574

1:5000 416.667 12.672 0.079 3.9856 0.2509 0.00624

1:5280 440.000 12.000 0.0833 4.4444 0.225 0.00694

1:6000 500.000 10.560 0.095 5.7392 0.1742 0.00897

1:6500 541.667 9.748 Ö.103 6.7356 0.1485 0.01054

1:7000 583.333 9.051 0.110 7.8117 0.1280 0.01219

1:7200 600.000 8.800 0.114 8.2645 0.1210 0.01291

1:7920 660.000 8.000 0.125 10.0000 0.1000 0.01563

1:8000 666.667 7.920 0.126 10.2030 0.0980 0.01596

1:8400 700.000 7.543 0.133 11.2489 0.0889 0.01758

1:9000 750.000 7.040 0.142 12.9132 0.0774 0.02018

1:9600 800.000 6.600 0.152 14.6924 0.0681 0.02296

1:10000 833.333 6.336 0.158 15.9423 0.0627 0.02489

1:10800 900.000 5.867 0.170 18.5950 0.0538 0.02905

1:12000 1000.000 5.280 0.189 22.9568 0.0436 0.03587

1:13200 1100.000 4.800 0.208 27.7778 0.0360 0.04340

1:14400 1200.000 4.400 0.227 33.0579 0.0303 0.05165

1:15000 1250.000 4.224 0.237 35.8701 0.0279 0.05605

1:15600 1300.000 4.062 0.246 38.7971 0.0258 0.06062

1:15840 1320.000 4.000 0.250 40.0000 0.0250 0.06250

1:16000 1333.333 3.960 0.253 40.8122 0.0245 0.06374

1:16800 1400.000 3.771 0.265 44.9954 0.0222 0.07031

1:18000 1500.000 3.520 0.284 51.6529 0.0194 0.08071

1:19000 1583.333 3.335 0.300 57.5515 0.0174 0.08989

1:19200 1600.000 3.300 0.303 58.7695 0.0170 0.09183

1:20000 1666.667 3.168 0.316 63.7690 0.0157 0.09968

1:20400 1700.000 3.106 0.322 66.3453 0.0151 0.10366

1:21120 1760.000 3.000 0.333 71.1111 0.0141 0.11111

1:21600 1800.000 2.933 0.341 74.3802 0.0134 0.11622

1:22200 1850.000 2.854 0.350 78.5698 0.0127 0.12277

1:22800 1900.000 2.779 0.360 82.8742 0.0121 0.12949

1:24000 2000.000 2.640 0.379 91.8274 0.0109 0.14348

1:25000 2083.333 2.534 0.395 99.6391 0.0100 0.15564

1:31680 2640.000 2.000 0.500 160.0000 0.0063 0.25000

1:36000 3000.000 1.760 0.568 206.6116 0.0048 0.32283

1:40000 3333.333 1.584 0.631 255.0760 0.0039 0.39484

1:48000 4000.000 1.320 0.758 367.3095 0.0027 0.57392

1:50000 4166.667 1.267 0.789 398.5563 0.0025 0.62284

1:60000 5000.000 1.056 0.947 573.9210 0.0017 0.89675

1:62500 5208.333 1.014 0.986 622.7442 0.0016 0.97291

1:63360 5280.000 1.000 1.000 640.0000 0.0016 1.00000

1:70000 5833.333 0.905 1.105 781.1703 0.0013 1.22044

1:96000 8000.000 0.660 1.515 1469.2378 0.0007 2.29568

1:120000 10000.000 0.528 1.894 2295.6841 0.0004 3.58700

1:125000 10416.667 0.507 1.973 2490.9800 0.0004 3.89165

1:126720 10560.000 0.500 2.000 2560.0000 0.0004 4.00000

1:144000 12000.000 0.440 2.273 3305.7851 0.0003 5.16529

1:250000 20833.333 0.253 3.946 9963.9070 0.0001 15.56811

Scale 63360 Scale (Scale)2 43560x144 (Ft. per In.)

Formulas^ 12 Scale 63360 43560x144 (Scale)2 (5280)2

'• Scale is the relation between distance on an airphoto and distance on the ground. It is expressed as a ratio

as shown here (1:20,000; that is, 1" on an airphoto equals 20,000" on the ground) or as a fraction (l/20,000).

Scale of vertical airphotos is derived by dividing the altitude of the camera above ground (not sea) level by

the focal length of the camera, and multiplying the quotient by 12.

38
TABLE 4.—MAJOR VERTICAL AERIAL PHOTOGRAPHIC COVERAGE FOR FAIRFAX CO., VA., 1950-1965

Area

covered

Year

flown

Approximate

negative

scale

Camera

focal

length

Approximate

contact

print scale

Approximate

scale of

enlargements

Prints

available from-^

Entire area Summer 1965 1:36,000 6" 1"=3,000' Up to 1"=750' Air Photographies

Most of area Oct. 1964 1:24,000 6" 1"=2,000' Up to 1"=500' U.S. Geological Survey

Entire area Feb. - Mar. 1964 1:12,000 6" 1"=1,000' Up to 1"=250' Air Photographies

Entire area Mar.-May 1963 1:36,000 6" 1"=3,000' Up to 1"=750' Aero Service

Most of area April 1963 1:36,000 6" 1"=3,000' Up to 1"=750' U.S. Geological Survey

Entire area 1963-1964 1:24,000 6" 1"=2,000• Up to 1"=500' U.S. Geological Survey

Part of area Dec. 1962 1:24,000 6" 1"=2,000' Up to 1"=500' Air Photographies

Entire area 1962 1:20,000 8 1/4" 1"=1,667' Up to 1"=400' Agriculture Stabilization and Conservation

Service

Part of area May 1962 1:12,000 6" 1"=1,000' Up to 1"=250' Air Photographies

Entire area March 1962 1:12,000 6" 1"=1,000' Up to 1"=250' Air Photographies

Part of area May 1961 1:18,000 6" 1"=1,500' Up to 1.1=3751 Air Photographies

Entire area March 1960 1:12,000 6" 1"=1,000' Up to 1"=250' Air Photographies

Entire area 1959-60 1:60,000 6" 1"=5,000' Up to 1"=1250' U.S. Geological Survey

(Army Map Service

Photos)

Part of area 1959 1:120,000 3 1/4" 1: 10,000'2 Up to 1"=2500' Aero Service

Part of area July 1957 1:6,000 6" 1"=500' Up to 1"=125' Air Photographies

Entire area 1954 1:20,000 8 1/4" 1"=1,667' Up to 1"=400' Soil Conservation Serv.

Entire area 1951 1:36,000 6" 1"=3,000' Up to 1"=750' U.S. Coast & Geodetic

Survey

Aero Service, Air Photographies, U.S. Coast & Geodetic Survey, and Soil Conservation Service will make enlargements of portions of negatives up to 10 times the contact print scale. Maximum size enlargement is 40" x

40"; enlargements greater than those indicated in the table would have to be in more than one section.

In addition to major coverage listed above, coverage for Fairfax and Alexandria cities is available from

several firms. American Air Surveys, Inc., has coverage of city of Fairfax and vicinity, March 1960, 1:6,000,

enlargements up to 1"=100'; city of Alexandria and vicinity, April 1963, 1:18,000, enlargements up to 1"=300'

and 1:24,000, with enlargements up to 1"=400'; western 2/3 of city of Alexandria, April 1964, 1:6,000, enlargements up to 1"=100'. Mention of aerial photographic firms is for information only and does not imply the Department's endorsement of certain firms to the detriment of other firms,, or that those mentioned include all

such films.

TABLE 5.—AIRPHOTO MOSAICS AVAILABLE FOR FAIRFAX CO., VA., 1950-1965

Area

covered

Date

photos

taken

Date

mosaic

compiled

Type

Negative

scale of

mosaic

No. of

mosaic

sheets to

cover

area

Source

of

mosaic

Most of area Nov. 1963 1964 Semieontrolled 1:24,000

(l"=2000')

1 Air Photographic s-"-

Entire area 1954 1957 Controlled 1:63,360

(1"=5280')

3 Soil Conservation Service

Entire area 1954 1957 Controlled 1:20,000

(1"=1667')

21 Soil Conservation Service

^ Mention of an aerial photographic firm is for information only, and does not imply the Department's endorsement of certain firms to the detriment of others.

39
TABLE 6.—AIRPHOTO INDEX COVERAGE AVAILABLE FOR FAIRFAX CO., VA., 1950-1965

Area

covered

Date photos

taken

Approximate

scale of

photos

Approximate

scale of

index

No. index

sheets needed

to cover area

Source

of index^

Most of area Oct. 1964 1:24,000 1:62,500 7 U.S. Geological Survey

Entire area Feb.-Mar. 1964 1:12,000 1:24,000 12 Air Photographies

Entire area Mar.-May 1963 1:36,000 1:144,000 2 1 Aero Service

Most of area April 1963 1:36,000 1:125,000 4 U.S. Geological Survey

Entire area 1963-64 1:24,000 1:62,500 12 U.S. Geological Survey

Part of area May 1962 1:12,000 1:24,000 12 Air Photographies

Entire area May-July 1962 1:20,000 1:63,360 4 Agriculture Stabilization and

Conservation Service

Entire area March 1960 1:12,000 1:24,000 12 Air Photographies

Entire area 1954 1:20,000 1:63,360 3 Soil Conservation Service

Entire area 1951 1:36,000 1:250,000 1 U.S. Coast & Geodetic Survey

" Mention of aerial photographic firms is for information only, and does not imply the Department's endorsement of certain firms to the detriment of other firms, or that those "mentioned include all such firms.

^ Included on one photo index sheet are all of Washington, D.C.; part of Montgomery Co., and all of Prince

Georges Co., Md.; all of Arlington and Fairfax Counties, most of Prince William Co., and part of Loudoun Co.,

Va.

TABLE 7.—SOURCES OF ILLUSTRATIONS

Figure

number

Identification

number Type; Scale, if any Place Date Source

Cover,

upper

half... Pa.-79,782 Low oblique Chester Co., Pa. Sept. 1950 ses

Cover,

lower

half... 40,905 High oblique Philadelphia, Pa. April 1963 SCS

1 SCS-Ia-2758 High oblique Templeton, Carroll Nov. 1961 Inf. USDA

Co., Iowa

2 MD. 30383 Low oblique Belair, Prince Georges Oct. 1962 Inf. USDA

Co., Md.

3 Lehigh Co.,

Sheet No.

pa.,

21

Soil map, 1:15,840 Lehigh Co., Pa • 1962 ses

4 BXI-1-12 Vertical, 1:20,000 Morton, Tazewell Co • y June 1939 National

111. Archives

(ASCS

photo)

5 BXI-lT-41 Vertical 1:20,000 Morton, Tazewell Co ' Í Aug. 1957 ASCS

111.

6 MD-RC-1-85 Vertical 1:6,000 Rock Creek Watershed,

Montgomery Co., Md.

Mar. 1957 ses

7 Photo-Index Sheet

No. 2, Prince

Georges Co., Md.

Photo Index, 1:63,360 Prince

Md.

Georges Co., Photos,

Oct. 1963

ASCS

8 AHV-7K-12 Vertical, 1:20,000 Prince Georges Co., Md. Oct. 1952 ASCS

9 AHV-2T-12 Vertical, 1:20,000 Prince Georges Co., Md. June 1957 ASCS

10 AHV-3DD-188 Vertical, 1:20,000 Prince Georges Co., Md. Oct. 1963 ASCS

11 AHV-3DD-188 Vertical, 1:12,000 Prince Georges Co., Md. Oct. 1963 ASCS

12 AHV-3DD-188 Vertical, 1:7,200 Prince Georges Co., Md. Oct. 1963 ASCS

13 AHV-3DD-188 Vertical, 1:4,800 Prince Georges Co., Md. Oct. 1963 ASCS

14 Photomosaic sheet Semicontrolled mosaic. Prince Georges Co., Md. Photos, Oct. 1963 (ASCS)

8-13, Prince Georges 1:15,840 Mosaic, 1964 ses

Co., Md.

40 •U U. S. GOVERNMENT PRINTING OFFICE : 1966 O - 217-583