USGS DIGITAL CARTOGRAPHIC DATA STANDARDS 

USGS Circular 895-A: overview and USGS Activities 

B: Digital Elevation Models 

C: Digital Line Graphs from 1:24,000-Scale Maps 

D: Digital Line Graphs from 1:2,000,000-Scale Maps 

E: Land Use and Land cover Digital nata 

F: Geographic Names Information System 

G: Digital Line Graph Attribute Coding Standards 

Questions regarding availability and ordering of US Geonata (all 

types of digital cartographic and geographic data produced and 

distributed by the u.s. Geological survey) should be addressed to: 

user Services Section 

National Cartographic Information Center 

u.s. Geological survey 

507 National Center 

Reston, Virginia 22092 

Technical questions and comments should be addressed to: 

Chief, National Mapping Division 

u.s. Geological survey 

516 National Center 

Reston, Virginia 22092 

Any use of trade names and trademarks in this publication is for 

identification purposes only and does not constitute endorsement by the 

u.s. Geological survey. 
DIGITAL ELEVATION MODELS 

By Atef A. Elassal and Vincent M. Caruso 

USGS Digital cartographic Data standards 

Edited by Robert B. McEwen, Richard E. Witmer, and Benjamin s. Ramey 

Geological survey Circular 895-B 

1983 
United States Department of the Interior 

WILLIAM P. CLARK, Secretary 

Geological Survey 

Dallas L. Peck, Director 

Library of Congress Cataloging in Publication Data 

Main entry under title: 

USGS digital caartographic data standards. Digital elevation models. 

(U.S. Geological Survey circular; 895-8) 

Bibliography: p. 

Supt. of Docs. no.:l 19.4/2:895-8 

1. Digital mapping-Standards. 2. United States-AititudesA. Geological Survey (U.S.) II. U.S.G.S. digital cartographic 

standards. Digital elevation models. Ill. Series: Geological Survey circular; 895-8. 

GA139.U83 1983 526 83-600191 

Free on application to Distribution Branch, Text Products Section, 

U.S. Geological Survey, 604 South Pickett Street, Alexandria, VA 22304 
FOREWORD 

In recent years, the disciplines of cartography and geography have undergone a rapid and striking reorientation as the 

techniques for digital collection and manipulation of data have 

evolved from fledgling laboratory procedures into dominant and 

driving forces that now pervade the disciplines. Digital techniques have provided a variety of new and powerful capabilities 

to collect, manipulate, analyze, and display spatial data. 

However, this evolution also has introduced a number of new and 

complex problems. One of the most pressing problems, and one 

which is receiving particular attention at present, is the issue 

of digital cartographic data standards. 

The u.s. Geological survey (USGS) has been actively 

developing digital cartographic and geographic techniques for 

over a decade and has taken significant steps to develop and 

define in-house standards governing the various types of 

digital cartographic data that are being collected and archived 

in a national digital cartographic data base. The in-house 

standards are expressed in the form of specifications documents 

that were prepared to govern collection of the data and in the 

form of user guides that were prepared for distribution with 

the data. 

In an effort to fulfill lead agency requirements for 

promulgation of Federal standards in the earth sciences, the 

documents have been assembled with explanatory text into this 

USGS Circular consisting of separately bound chapters. This 

Circular describes some of the pertinent issues relating to 

digital cartographic data standards, documents the digital 

cartographic data standards currently in use within the USGS 

National Mapping Division, and details USGS efforts to define 

national digital cartographic data standards. 

Chapter A is an overview in which the major issues involved 

in developing digital cartographic data standards are discussed 

and the activities of the USGS related to digital cartographic 

data production and standards development are described in 

detail. Succeeding chapters comprise the pertinent documents 

that establish USGS in-house standards for the various types of 

digital cartographic data currently produced by the National 

Mapping Division; that is, digital elevation data, digital 

planimetric data, digital land use and land cover data, and 

digital geographic names data. 

This compendium of relevant material is prepared to serve 

as a benchmark and to assist ongoing efforts to establish 

acceptable standards and conventions for both Federal agencies 

and the public. 

Dallas L. Peck 

Director, 

u.s. Geological survey 

Department of the Interior 

iii 

R. B. southard 

Chief, 

National Mapping Division 

u.s. Geological survey 
PREFACE 

This Circular is the result of the efforts of numerous individuals who have contributed to the research, development, and 

preparation of various digital cartographic and geographic standards for the National Mapping Division of the u.s. Geological 

survey. The individuals named as chapter authors represent both 

the originators of the various concepts as well as the writers 

who expanded and clarified these ideas. Their contributions, 

either to the concepts or the writing, are of such magnitude as 

to warrant crediting as authors. 

Atef A. Elassal was largely responsible for the original 

data structures and computer file formats that are used for the 

digital line graphs and digital elevation models. The attribute 

coding scheme was first developed by members of the Digital 

Applications Team under the direction of Robert B. McEwen. The 

Geographic Names Information System was conceived and developed 

by Sam Stulberg and Roger L. Payne. The Geographic Information 

Retrieval and Analysis system was developed by Robin G. Fegeas, 

K. Eric Anderson, Stephen c. Guptill, Cheryl A. Hallam, and 

William B. Mitchell. The small-scale digital line graph data 

structure and attribute coding scheme was developed by warren E. 

Schmidt and Michael A. Domaratz. 

The Circular was compiled in part from various user guides 

and technical instructions of the National Mapping Division. 

These documents were originally prepared by several individuals; 

credit is acknowledged to G. Michael Callahan, A. Joan Szeide, 

William R. Allder, Vincent M. caruso, Hugh w. calkins, Donna 

Cedar-southworth, and Cheryl A. Hallam. The compilation of the 

various guides, instructions, and other material into the 

Circular format was performed with major assistance by Clark H. 

Cramer, Eloise R. Byrd, and Cynthia L. cunningham. 

We acknowledge these substantial contributions that have led 

to this publication. 

iv 
CONTENTS 

Page 

Foreword ••••••••••••••••••••••••••••••••••••••••••••••••••• iii 

Preface •••••••••••••••••••••••••••••••••••••••••••••••••••• iv 

Abstract ••••••••••••••••••••••••••••••••••••••••••••••••••• 1 

Introduction ••••••••••••••••••••••••••••••••••••••••••••••• 1 

7.5-minute digital elevation models •••••••••••••••••••••••• 2 

Characteristics •••••••••••••••••••••••••••••••••••••••• 2 

Data production •••••••••••••••••••••••••••••••••••••••• 2 

1:250,000-scale digital elevation models ••••••••••••••••••• 4 

Characteristics •••••••••••••••••••••••••••••••••••••••• 4 

Data production •••••••••••••••••••••••••••••••••••••••• 4 

Geometry ••••••••••••••••••••••••••••••••••••••••••••••••••• 5 

Accuracy ••••••••••••••••••••••••••••••••••••••••••••••••••• 5 

Editing •••••••••••••••••••••••••••••••••••••••••••••••••••• 5 

Data records ••••••••••••••••••••••••••••••••••••••••••••••• 9 

sample data records •••••••••••••••••••••••••••••••••••• 9 

sample applications •••••••••••••••••••••••••••••••••••••••• 9 

Appendix A. DEM data elements--logical record type A 20 

Appendix B. DEM data elements--logical record type B 23 

Appendix c. DEM data elements--logical record type c 25 

Appendix D. sample quadrilateral coordinates •••••••••••••• 26 

Appendix E. Codes for State plane coordinate zones •••••••• 27 

Appendix F. Universal Transverse Mercator zone locations 

and central meridians •••••••••••••••••••••••••••••••••••• 29 

Appendix G. Parameters required for definition of map 

projections •••••••••••••••••••••••••••••••••••••••••••••• 30 

Appendix H. Digital terrain tapes ••••••••••••••••••••••••• 35 

ILLUSTRATIONS 

Page 

Figure 1. structure of a 7.5-minute digital elevation 

model •••.••••..••••••••.••••••••• , • . • • . • • • . • • • 3 

2. structure of a 1:250,000-scale digital elevation 

model ••••••••••••••••••••••••••••••••••••••••• 4 

3. Computation of first data point in a DEM west of 

the central meridian •••••••••••••••••••••••••• 6 

4. Computation of first data point in a DEM east of 

5. 

6. 

the central meridian •••••••••••••••••••••••••• 

Geometry and nomenclature of the DEM file ••••••• 

Pre-eruption isometric plot of Mount St. Helens 

7 

8 

DEM ••••••••••••••••••••••••••••••••••••••••••• 17 

7. Post-eruption isometric plot of Mount St. Helens 

DEM ••••••••••••••••••••••••••••••••••••••••••• 18 

v 
TABLES 

Table 1. sample DEM type A logical records--Mount 

st. Helens NW, washington, quadrangle 

Page 

(7.5-minute) ••••••••••••••••••••••••••••••••••• 10 

2. Sample DEM type B logical records--Mount 

st. Helens NW, washington, quadrangle 

(7.5-minute) ••••••••••••••••••••••••••••••••••• 12 

3. sample DEM type c logical records--Mount 

st. Helens NW, washington, quadrangle 

(7.5-minute) ••••••••••••••••••••••••••••••••••• 13 

4. Sample DEM type A logical records--Reno, NevadaCalifornia, quadrangle (west half) (1:250,000-

scale) . • • • • • • • • . • . . . . • • • • . . . . • • . . . • • • • • • . • . . • • • 14 

5. Sample DEM type B logical records--Reno, NevadaCalifornia, quadrangle (west half) (1:250,000-

scale) • • • • • • • . • • • • . • • • • • • • • • • • • • • • • • • • • • • • . • . • • 16 

vi 
USGS Digital Cartographic Data Standards 

DIGITAL ELEVATION MODELS 

By Atef A. Elassal and Vincent M. Caruso 

Abstract 

The discipline of cartography is 

undergoing a number of profound changes 

that center on the emerging influence of 

digital manipulation and analysis of 

data for the preparation of cartographic 

materials and for use in geographic information systems. Operational requirements have led to the development by the 

USGS National Mapping Division of several 

documents that establish in-house digital 

cartographic standards. 

In an effort to fulfill lead agency 

requirements for promulgation of Federal 

standards in the earth sciences, the 

documents have been edited and assembled 

with explanatory text into a USGS 

Circular. This Circular describes some 

of the pertinent issues relative to 

digital cartographic data standards, 

documents the digital cartographic data 

standards currently in use within the 

USGS, and details the efforts of the USGS 

related to the definition of national 

digital cartographic data standards. It 

consists of several chapters; the first 

is a general overview, and each succeeding chapter is made up from documents 

that establish in-house standards for one 

of the various types of digital cartographic data currently produced. This 

chapter, 895-B, describes the digital 

elevation model data produced and 

distributed by USGS and similar data at 

a smaller scale produced by the Defense 

Mapping Agency and distributed by USGS. 

INTRODUCTION 

The u.s. Geological survey (USGS) 

distributes digital cartographic and 

geographic data as part of the National 

Mapping Program. One of the several 

types of data distributed is digital 

elevation data, which consists of arrays 

of elevations, usually at regularly 

spaced intervals, for a number of ground 

positions. 

This document describes two distinct 

digital elevation data products that are 

distributed by the USGS in the standard 

digital elevation model (DEM) tape 

format: ( 1) DEM' s produced by the USGS 

that correspond in coverage to standard 

1:24,000-scale 7.5- x 7.5-minute quadrangles. This type of digital elevation 

data is referred to in this document as 

7.5-minute DEM data. (2) DEM's produced 

by the Defense Mapping Agency (DMA) that 

correspond in coverage to 1° x 1° blocks 

(one half of standard 1:250,000-scale 1° 

x 2° quadrangles). This type of digital 

elevation data is referred to in this 

document as ·1: 250., 000-scale DEM data. 

The 7.5-minute DEM data files and 

the 1:250, 000-scale DEM data files are 

identical in logical data st-ructure but 

differ in sampling interval, geographic 

reference system, areas covered, and 

accuracy of data. USGS 7. 5-minute DEM 

data are available for selected quadrangles in the United States; DMA 

1:250,000-scale DEM data are available 

for most of the United States. 
The USGS also distributes another 

type of digital elevation data--

l: 250, 000-scale terrain/planar digital 

data (digital terrain tapes). Digital 

terrain tapes are a product of the 

Defense Mapping Agency and correspond in 

coverage to one half of a standard 

1:250,000-scale 1° x 2° quadrangle. 

Digital terrain tapes are distributed, as 

produced by the DMA, and do not conform 

to the standard DEM tape format. Information on digital terrain tapes is provided in Appendix H. 

7.5 MINUTE DIGITAL ELEVATION MODELS 

CHARACTERISTICS 

A 7 .5-minute DEM has the following 

characteristics: 

• The data consist of a regular array 

of elevations referenced in the 

Universal Transverse Mercator (UTM) 

coordinate system. Elevations 

randomly located in an irregular 

array also are allowed in the file 

structure, but only regular arrays 

have been produced to date. 

• The unit of coverage is the 7.5-

minute quadrangle. overedge coverage 

is not provided. 

• The data are ordered from south to 

north in profiles that are ordered 

from west to east. 

• The data are stored as profiles in 

which the spacing of the elevations 

along and between each profile is 

30 m. 

• The profiles do not always have the 

same number of elevations due to the 

variable angle between true north 

and grid north of the UTM coordinate 

system. 

The generation of profiles for 7.5-

minute DEM's is accomplished using a UTM 

cartesian coordinate system as a base. 

The profiles are clipped to the straight 

line intercept between the four geographic corners of the quadrangle--an 

2 

approximation of the geographic map 

boundary (neatline). The resulting area 

of coverage for the DEM is a quadrilateral, the opposite sides of which are 

not parallel. ( s~e Appendix D for an 

example of UTM coordinates describing a 

7.5-minute quadrilateral figure.) 

The UTM coordinates of the DEM's four 

corners (bounds) are listed in the type 

A record, data element 10, and the UTM 

coordinates of the starting points of 

each profile are listed in the type B 

record (profiles), data element 3 (see 

pages 21 and 23). These coordinates 

describe the shape of the quadrilateral 

and the variable x,y starting position of 

each profile. Because of the variable 

orientation of the quadrilateral, in 

relation to the UTM coordinate system, 

profiles intersect the east and west 

neatlines as well as the north and south 

neatlines. The intersections result in 

a regular stair-stepped arrangement of 

the 30-m nodes just inside the neatline. 

DATA PRODUCTION 

The 7.5-minute DEM data are produced 

in 7. 5- x 7. 5-minute blocks either from 

map contour overlays that have been digitized or from automated or manual scanning of photographs usually taken at an 

average height of 40,000 ft. ( 1:80,000-

scale). The data are processed to produce a DEM with a 30-m sampling interval. 

The structure of a 7 .5-minute DEM data 

file is shown in figure 1. (See pages 

10- 13 for sample data records.) 

The USGS uses three systems to 

collect the • digital elevation data for 

production of 7.5-minute DEM's: (1) the 

Gestalt Photo Mapper I I ( GPM2): ( 2) 

manual profiling from stereomodels; and 

(3) the Digital cartographic Software 

System (DCASS). 

The GPM2 is a highly automated photogrammetric system designed to produce 

orthophotos, digital terrain data, and 

contours. An electronic image correlation component of the GPM2 measures the 

parallax of 2,444 points within each 

9- x 8-mm area of a photogrammetric 

stereomodel. Of these 2, 444 correlated 

points, subunits of 576, 1,024, or 1,600 

points are collected for inclusion in the 
0> 

c:: 

:c 

t:: 

0 

z 

Pt 2 

~x = 30 meters (Easting) 

~y = 30 meters (Northing) 

0 = Elevation point in 

adjacent quadrangle 

• = Elevation point 

e = First point along profile 

D = Corner of DEM polygon 

(7.5-minute quadrangle corners) 

(Example is a quadrangle west of 

central meridian of UTM zone.) 

Figure 1.--structure of a 7.5-minute digital elevation model. 

elevation model. These subunits are 

called patches, and the patch size is 

selected to accommodate various terrain 

conditions. The horizontal (x and y) 

spacing of the elevation points within 

each patch is approximately 182 micrometers at photo scale (equivalent to ~ 

ground distance of approximately 4 7 ft. 

when using photographs at 1:80,000 

scale). Each of the two stereomodels 

used to cover a standard 7.5-minute quadrangle contains over 500,000 correlated 

points; these are regridded to form a 

DEM in the standard format. 

The manual profiling systems use 

stereoplotters, interfaced with electronic digital profile recording modules, 

for scanning of stereomodels in the photo 

y direction. High-altitude aerial photographs are used as source material. The 

scan speed and slot size (stepover interval) can be selected by the operator to 

accommodate steepness in topographic 

slope. The most commonly used slot size 

is 4-mm, which results in elevation profiles spaced approximately 90-m apart. 

3 

Elevations are normally recorded every 

30-m along each profile. The profiled 

elevation data are reformatted and 

regridded to a regular 30-m UTM spacing, 

written in standard DEM format, and 

tested for vertical accuracy before 

placement in the National Digital 

cartographic Data Base (NDCDB). Digital 

profile data are collected in this manner 

as companion products with the production 

of orthophotos. 

The DCASS forms a DEM from digitally 

encoded vector contour data. Stereoplotters, equipped with three-axis 

digital recording modules, are used to 

collect vector contour data while the 

instruments are being used for photogrammetric stereocompilation of 1:24,000-

scale quadrangle maps. During the acquisition phase, the contours are assigned 

elevation values (attributes). The 

vector contour data are processed into 

profile lines and the elevation matrix at 

a 30-m spacing is formed using a bilinear 

interpolation between the intersections 

of the lines with the contour vectors. 
1:250,000-SCALE DIGITAL ELEVATION MODELS 

CHARACTERISTICS 

A 1:250, 000-scale DEM in the United 

States (except Alaska) has the following 

characteristics: 

• The data consist of a regular array 

of elevations cast on the geographic 

(latitude/longitude) coordinate 

system. 

• 

• 

• 

• 

The unit of coverage is a 1 o x 1 o 

block representing one-half of a 1° x 

2° 1:250,000-scale map. The unit of 

coverage includes profiles coincident 

with the neatlines of the map. 

The data are ordered as profiles 

ascending northward. The or1g1n is 

at the southwest corner of the map. 

The data are stored as profiles in 

which the spacing of the elevations 

along and between each profile is 3 

arc-seconds. 

The data comprise an array having 

1,201 profiles with 1,201 elevations 

per profile. 

Q) 

"'0 

. .e 

co 

.....J 

Longitude 

For the State of Alaska, the spacing 

of elevations along each profile is 3 

arc-seconds (1,201 elevations per profile), and the normal spacing between 

profiles varies from 6 arc-seconds (601 

profiles per DEM) in the south to 12 arcseconds ( 151 profiles per DEM) on the 

north slope of the state. some Alaska 

sheets have a 4-arc-second spacing of the 

profiles. 

DATA PRODUCTION 

The 1:250,000-scale DEM data are produced by interpolating elevations at intervals of 3 arc-seconds from contours, 

ridgelines, and drains digitized from 

1:250,000-scale topographic maps. Three 

seconds of arc represents approximately 

90 m in the north-south axis and a variable dimension (approximately 90 m at the 

equator to 60 m at 50° latitude) in the 

east-west axis due to convergence of the 

meridians. The area of each map is 

divided into an east half and a west half 

to accommodate the large volume of data 

required to cover the 1° x 2° topographic 

map area. The structure of a 1:250,000-

scale DEM data file is shown in figure 2 • 

(See pages 14 16 for sample data 

records.) 

Ax = 3 arc-seconds 

A y = 3 arc-seconds 

0 = Elevation point in 

Pt 4 

adjacent 1 o block 

• = Elevation point 

e = First point along profile 

0 = Corner of OEM polygon 

W block, scale 1 :250,000) 

Figure 2.--structure of a 1:250,000-scale 

digital elevation model. 

4 
GEOMETRY 

Profiles are the basic building 

blocks of DEM 1 s and are defined as onedimensional patches, that is, arrays of 

dimension m rows x n columns, where m is 

the length of the profile (variable 

length for 7.5-minute DEM 1 s or fixed 

length for 1:250, 000-scale DEM 1 s) and n 

is set to 1. 

Figure 3 provides an example of the 

computation for the first data point 

inside the quadrilateral representing a 

7. 5-minute DEM west of the UTM central 

meridian. Figure 4 provides a similar 

example for a quadrangle east of the 

central meridian. 

Figure 5 illustrates the internal 

relationship of elevations ordered as 

profiles in which the spacing of the 

elevations along each profile is Ay and 

the spacing between profiles is Ax. 

Figure 5 also relates the internal array 

structure to actual ground coordinates 

(XGP' YGp), based on an or1g1n of 

the DEM at the lower left corner (XG0 , 

YG0 ), and a rotation angle, if any 

(the rotation angle of 7. 5-minute DEM 1 s 

is normally set to zero). 

ACCURACY 

The accuracy of digital elevation 

models is partially dependent on the 

scale of the source materials from which 

the data are obtained. For example, the 

accuracy of 1:250,000-scale DEM 1 s is consistent with the accuracy of the contours 

(50 ft. in flat terrain, 100 ft. in 

moderate terrain, and 200 ft. in steep 

terrain) on the 1:250,000-scale topographic maps used to produce the data. 

The accuracy of 7.5-minute DEM 1 s depends 

on the data source (either aerial photographs, or contours on 7. 5-minute maps 

of the USGS Topographic Map Series). 

Vertical accuracy of 7.5-minute DEM 1 s 

derived from aerial photographs is highly 

dependent on the original resolution and 

contrast of the source photographs, as 

well as the presence of natural or manmade features and an abundance of survey 

control for constraining the stereomodels. Vertical accuracy of 7.5-minute 

DEM 1 s derived from contours is consistent 

5 

with the accuracy of the contours on the 

source map. The 7.5-minute DEM 1 s are 

stored in one of the two separate DEM 

data bases in the NDCDB, depending on 

tested vertical accuracy. Accuracy is 

either less than 7-m vertical RMSE, or 

7- to 15-m vertical RMSE. The 7-m RMSE 

was determined to be a 

standard for DEM 1 s derived 

altitude aerial photographs 

40,000 ft. (1:80,000-scale), 

reasonable 

from hightaken at 

attainable 

under a variety of terrain conditions 

and instrument constraints. 

The methods used for determining 

vertical accuracy of 7.5-minute DEM's 

differ with the collection method. For 

DEM 1 s collected with the GPM2, a weighted 

root mean square error (RMSE) value is 

derived from the relative elevation 

differences between patch joins and the 

relative elevation difference between 

coincident points in the overlay area of 

the two stereomodels covering a quadrangle. The RMSE of the elevation data 

derived from the manual profiling and 

the DCASS systems, however, is computed 

by comparing known ground vertical 

control elevations (for a minimum of 10 

discrete image points) to linearly 

interpolated DEM elevation points. 

EDITING 

All DEM data are classified into one 

of three levels depending on editing, 

enhancements, and spatial structuring: 

Level 1 - Raw elevation data sets in 

a standardized format. Only 

gross blunders in data 

capture have been eliminated. 

Level 2 - Elevation data sets that 

have been smoothed for 

consistency and edited to 

remove random errors. 

Level 3 - Elevation data sets that 

have been edited and modified to insure positional 

consistency with planimetric 

data categories such as hydrography and transportation. 
E 

ci 

§ 

g 

II 

)( 

Example computation of UTM coordinates 

Cx1,v1> of the first data point in a 

7.5-minute DBM west of the central 

meridian. 

The southwest corner of the 7.5- minute 

DBM used in this example ls at latitude 

27"15'00", longitude -94"37'30" (x 

339117.754m, ysw = 3015002.066oi'f. 

Compute x coordinate cx1

) of the first 

profile. The first profile is offset to the 

next integer multiple of 30m east of the 

soutwest corner. 

~ 339117.754m 

30m 30m 

= 11303.9 (round up) 

= 11304 

x 1 = 11304 (30m) 

= 339120m 

Compute y coordinate Cy1

) of the first data 

point on the first profile. The first data 

point is offset to the next integer multiple 

of 30m north of the southwest corner. 

~ = 3015002.066m 

30m 30m 

= 100500.07 (round up) 

= 100501 

v1 = 100501 (30m) 

= 3015030m 

Figure 3.--computation of first data point in a DEM 

west of the central meridian. 

6 
c: 

as 

'0 

-~ E 

6 ~ 0 

1!! 0 

0 

E 0 LO Q) 

() II 

~ >< 

I-

:::> 

first data point 

(x,, y,) 

Example computation of UTM coordinates 

Cx1

,y1l of the first data point in a 

7 .5-minute DBM east of the central 

meridian. 

The southwest corner of the 7.5-minute 

DBM used in this example is at latitude 

27°07'30", longitude -92°30'00" (xsw 

=549553.918m, ysw=3000211.052ml. 

The northwest corner is at latitude 

27°15'00", longitude -92°30'00" (xnw 

=549498. 713m, ynw =3014056.068ml. 

Compute x coordinate (x1l of the first. 

profile. The first profile is offset to the 

next integer multiple of 30m east of the 

northwest corner. 

X 

nw 

30m 

= 549498. 713m 

30m 

= 18316.6 (round upl 

= 18317 

= 18317 (30ml 

= 549510m 

Compute y coordinate (y 1

1 of the first data 

point on the first profile. The first 

data point is offset to the next integer 

multiple of 30m north of the intercept (yintl 

of the first profile with the western 

longitude line of the 7 .5-minute quadrangle. 

Cal Use the slope intercept formula y=mx+b 

to compute yint" 

m = (ynw-Yswl/(xnw-xsw1 

= 13845.016/-55.205 

(bl Compute y 1 

Yint 

30ni 

b = Ysw- mxsw 

= 3000211.052m- [C-250.79)(549553.919)] 

= 140822838.147m 

= b + mx1 = 140822838.147m + [(-250.79l(549510ml] 

= 3011225.247m 

= 3011225.247m 

30m 

= 100374.175 (round upl 

= 100375 

= 100375 (30ml 

= 3011250 

Figure 4.--computation of first data point in a DEM 

east of the central meridian. 

7 
y 

(1) 

Xp = (i-1) t:J..x 

YP = 0-1)6.y n columns 

(2) 

Figure 5.--Geornetry and nomenclature of the DEM file. 

8 
virtually all of the 7.5-minute DEM 1

S 

produced to date are considered to be 

level 1. Only the limited number of 7.5-

minute DEM 1 s generated by interpolation 

from digital contours are presently considered to be level 2. The USGS does not 

currently produce level 3 DEM data. 

All 1:250 ,000-scale DEM 1 s have been 

classified as level 3, although the 

primary source materials, 1:250,000-scale 

topographic maps, are more generalized 

than the 7.5-minute DEM sources. The 

level 3 designation reflects inclusion 

of planimetric features as constraints 

in the DMA gridding process and also 

reflects editing, where needed, to insure 

agreement with the 1:250,000-scale source 

materials. 

DATA RECORDS 

A DEM file is organized into a series 

of three logical records formatted as 

shown in Appendixes A-C. Appendixes D-G 

consist of code definitions that are 

needed to interpret various data elements 

in the three records. The type A record 

contains information defining the general 

characteristics of the DEM, including 

descriptive header information relating 

to the DEM 1 s name, boundaries, scale, 

units of measurement, minimum and maximum 

data values, number of type B records, 

and projection parameters. There is only 

one type A record for each DEM file, and 

it appears before any other record. The 

type B record contains elevation data and 

associated header information. All type 

B records of the DEM files currently 

being distributed are made up of data 

from one-dimensional bands called profiles. Therefore, the number of complete 

profiles covering the DEM area is synonymous with the number of type B records 

9 

in the DEM. The type c record contains 

statistics on the accuracy of the data in 

the file. 

SAMPLE DATA RECORDS 

Following are sample sets of A, B, 

and c records, corresponding to a typical 

7. 5-minute DEM (tables 1-3), and sample 

sets of A and B records for a typical 

1:250,000-scale DEM (tables 4, 5). Included in these samples are literal ASCII 

listings of records directly from DEM 

distribution tapes. Following the 

literal listings are tabular explanations 

of each element in the type A, B, and c 

records. The tabular explanations may be 

used as direct references between the 

literal listings and the logical record 

type formats shown in Appendixes A-C. 

Appendixes D-G consist of code definitions that are needed to interpret various data elements in the three records. 

SAMPLE APPLICATIONS 

The DEM files may be used in the generation of graphics such as isometric 

projections displaying slope, direction 

of slope, and terrain profiles between 

designated points. They may also be used 

in combination with other data types, for 

example, with stream locations and 

we~ther data to plan forest fire control 

or with remote sensing data to classify 

vegetation. Many nongraphic applications 

such as modeling terrain gravity data for 

use in locating energy resources, determining the volume of proposed reservoirs, 

calculating the amount of material removed during strip mining, and determining landslide probability have also been 

developed. Figures 6 and 7 show two 

graphic applications of DEM 1 s. 
...... 

0 

Table !.--Sample DEM Type A Logical Record--Mt. st. Helens NW, 

Washington, Quadrangle (7.5-minute) 

KT ST HELENS NW,WA. SPIRIT LAKE FH:20000 KSH-K80 3-176 09/06/80 B-8 N=2.00x1.00 s=2.00x1.00KM 9 PANEL FILES 30M x 30M INTERVAL 

1 1 1 10 0.0 0.0 0.0 0.0 0.0 

0.0 0.0 0.0 0.0 0.0 

0.0 0.0 0.0 0.0 0.0 2 2 

4 0.5579450118211330+06 0.5107991339017300+07 0.5578138139542320+06 0.5121880027532530+07 0.5674494203127150+06 

8469270+07 0.5676024874735990+06 0.5108090067132480+07 0.6790000000000000+03 0.2543000000000000+04 0.0 

0.512197873 

1 

0.300000E+020.300000+E020.100000E+01 1 327 

Data 

Element Content 

1 Mt. St. Helens 

NW, WA etc. 

2 1 

3 1 

4 1 

5 10 

6 o.o 

(15 sets of 0.0) 

7 2 

8 2 

9 4 

Explanation 

Quadrangle name field (144 characters) and other descriptive information 

relating to the digital production process. 

DEM level code. 

Pattern code indicating either a regular or random elevation pattern; 1 

indicates a regular pattern. 

Planimetric reference system code; 1 indicates UTM coordinate system. 

Code defining the zone in the ground planimetric reference system. 

Map projection parameters; all 15 fields are set to zero for the UTM 

coordinate system and should be ignored. 

Units code; 2 represents meters as the unit of measure for ground planimetric 

coordinates throughout the file. 

Units code; 2 represents meters as the unit of measure for elevation 

coordinates throughout the file. 

Number (n) of sides in the polygon which defines the coverage of the DEM file 

(usually equal to 4). 
...... 

...... 

Data 

Element 

10 

11 

12 

13 

14 

15 

Table 1.--Sample DEM Type A Logical Record--Mt. St. Helens NW, 

Washington, Quadrangle (7.5-minute)--continued 

Content 

0.5579450 ••• 0+06 

0.679 •••• D+03 

0.2543 ••• D+04 

o.o 

1 

0.3000000E+02 

0.3000000E+02 

O.lOOOOOOE+Ol 

1, 327 

Explanation 

A 4,2 array containing the ground coordinates of the four corners of the DEM. 

Translation to decimal format yields: 557945.0, 5107991.3; 557813.8, 

5121880.0; 567449.4, 5121978.7; 567602.5 5108090.1. 

Minimum and maximum elevations for the DEM. 

Counterclockwise angle (in radians) from the primary axis of ground 

planimetric reference to the primary axis of the DEM local reference system. 

Accuracy code; 1 indicates that a record of accuracy exists and is contained 

in record type c. 

A Three-element array containing DEM spatial resolution (x,y,z); usually set 

to 30, 30, 1. 

A Two-element array containing the number of rows and columns of profiles in 

the DEM. The row value m is usually set to 1 as an indication that the arrays 

are actually one dimensional profiles. The column value n equaling 327 

indicates that the DEM file consists of a total of 327 profiles. 
...... 

N 

Table 2.--sample DEM Type B Logical Record--Mt. St. Helens NW, 

washington, Quadrangle (7.5-minute) 

1 2 128 1 0.5578500000000000+06 0.5118060000000000+07 0.0 0.8900000000000000+03 0.12050000000 

0000+04 1202 1204 1203 1205 1205 1202 1198 1194 1191 1188 1185 1176 1170 1168 1166 1165 1167 1168 1167 1165 1160 

151 1158 1165 1163 1166 1170 1163 1159 1159 1154 1147 1144 1137 1130 1121 1110 1096 1098 1096 1088 1084 1081 1080 

1082 1084 1080 1071 1055 1045 1039 1040 1039 1035 1029 1025 1023 1021 1018 1010 1009 1011 1010 1007 1001 998 9 

6 996 992 988 993 995 995 994 991 983 979 977 970 965 961 955 950 948 953 958 931 943 936 

935 934 932 930 928 923 922 924 918 915 916 913 910 911 912 911 910 910 910 910 910 912 912 

913 911 910 911 911 912 910 909 910 907 904 900 898 895 890 890 

Data 

Element 

1 

2 

3 

4 

5 

6 

Content 

1' 2 

128, 1 

0.557850 ••• D+06 

0.5118060 ••• D+07 

o.o 

0.890 ••• D+03 

O.l205 •• D+04 

1202 1204 ••• 

. . . . . . . . . . . . . •••• 890 890 

Explanation 

Rows and column identification number of the profile contained in this record; 

1, 2 represents row 1, column 2, in the DEM data set • 

Number of rows (elevations) and columns in this profile; 128, 1 indicates 

there are 128 elevations and 1 column in this profile. 

Translated to the decimal, 557850.0 and 5118060.0 are the ground planimetric 

coordinates (UTM) of the first elevation in the profile. 

Elevation of local datum for the profile. 

Minimum and maximum elevations for the profile. 

An array of m x n elevations (m=l28, n=l) for the profile expressed in units of 

measure of meters (record A, element 8, indicates meters as units of measure) • 
0 0 0 

Data 

Element Content 

..... 1 0 w 

2 Three •o•s 

3 0 

4 1 

5 0' 0' 7 

6 0 

0 

Table 3.--sample DEM Type c Logical Record--Mt. St. Helens NW, 

washington, Quadrangle (7.5-minute) 

0 1 0 0 7 0 

Explanation 

Availability code; elements 1 through 3 relate to absolute accuracy and do not 

exist for this file. 

See above. 

See above. 

Availability code; 1 indicates that statistics are available in the next 

element. 

RMSE of DEM data relative to datum (in x, y, and z); the first two zeros 

indicate that the x and y relative statistics are not available. The value 7 

indicates that the DEM met relative vertical (z) accuracy criteria for the 7-m 

data base. 

Sample size code; 0 indicates that the relative statistic of element 5 is 

based on an estimated value. 
~ 

~ 

NJ11-01E W 

3 

Table 4.--sample DEM Type A Logical Records--Reno, Nevada-California, 

Quadrangle (West Half) (1:250,000-Scale) 

1 0 0 o.o o.o 0.0 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 2 

4 -0.428400000000000D+06 0.140400000000000D+06 -0.428400000000000D+06 0.144000000000000D+06 -0.424800000000000D+06 0.144000000 

OOOOOOD+06 -0.424800000000000D+06 0.140400000000000D+06 0.9990000000000000D+03 0.264100000000000D+04 0.0 0 

0.30000DE+010.300000E+010.100000E+01 1 1201 

Data 

Element Content 

1 NJll-OlE W 

2 3 

3 1 

4 0 

5 0 

6 o.o 

(15 sets of 0.0) 

7 3 

8 2 

9 4 

Explanation 

Quadrangle name field (144 characters); NJll-OlE W is the designation for the 

DEM covering the west half of the Reno, Nevada, sheet. 

DEM level code; 3 reflects processing by DMA which includes registration to 

planimetric features appearing on the source 1:250,000-scale topographic map. 

Pattern code; 1 indicates a regular elevation pattern. 

Planimetric reference system code; 0 indicates geographic coordinate system. 

zone code; there are no zones in the geographic system. Therefore, the zone 

code is set to zero. 

Map projection parameters; all 15 fields are set to zero for the geographic 

system and should be ignored. 

Units code; 3 represents arc-seconds as the unit of measure for ground 

planimetric coordinates throughout the file. 

Units code; 2 represents meters as the unit of measure for elevation 

coordinates throughout the file. 

Number (n) of sides in the polygon which defines the coverage of the DEM file 

(usually equal to 4). 
1-' 

U'1 

Data 

Element 

10 

11 

12 

13 

14 

15 

Table 4.--sample DEM Type A Logical Records--Reno, Nevada-California, 

Quadrangle (West Half) (1:250,000-Scale)--continued 

Content 

-04284 ••• D+06, 

O.l404 ••• D+06 

-0.4248 ••• D+06 

O.l404 ••• D+06 

0.9990 ••• D+03 

0.264l ••• D+04 

o.o 

0 

0.3000000E+01 

0.3000000E+Ol 

O.lOOOOOOE+Ol 

1, 1201 

Explanation 

A 4,2 array containing the ground coordinates of the four corners of the DEM. 

In this case translation from arc-seconds to degrees, minutes, and seconds 

yields: -119 00 00, 39 00 00; -119 00 00, 40 00 00; -118 00 00, 40 00 00; 

-118 00 00, 39 00 00. 

Minimum and maximum elevations· for the DEM. 

Counterclockwise angle from the primary axis of ground planimetric reference 

to the primary axis of the DEM local reference system. 

Accuracy code; 0 indicates that a record of accuracy does not exist and that 

no record type C will follow. 

A Three-element array containing DEM spatial resolution (x,y,z); usually set to 

3, 3, 1. 

A Two-element array containing the number of rows and columns of profiles in 

the DEM. The row value m is usually set to 1 as an indication that the arrays 

are actually one-dimensional profiles. The column value n set to 1,201 

indicates that the DEM file consists of a total of 1,201 profiles. 
t-' 

0'1 

Table 5.--sample DEM Type B Logical Record--Reno, Nevada-California, 

Quadrangle (West Half) (1:250,000-Scale) 

1 1 1201 1 -0.4284000000000000+06 0.1404000000000000+06 0.0 0.1212000000000000+04 0.177200000000+04 

00000+04 1538 1539 1539 1534 1529 1520 1513 1508 1501 1493 1488 1483 1479 1475 1474 1473 1472 1469 1469 1467 1466 

1464 

(As per 7.5-minute DEK's, element 6 contains elevations for the DKA OEM. 

This field always contains 1201 elements per 8.1 record.) 

1422 1417 1412 1405 1401 1396 1391 1392 1394 1397 1398 1397 1398 

1398 1397 1394 1390 1386 1383 1380 1377 1374 1372 1369 1367 1366 1367 1368 1368 1369 1369 1370 1371 1371 1371 

1371 137 

0 1371 1372 1370 1373 1373 1372 1376 1375 1374 1374 1372 

1372 1374 1374 1374 1374 1376 1378 1381 

Data 

Element 

1 

2 

3 

4 

5 

6 

Content 

1, 1 

1201, 1 

-0.4284 ••• D+06 

0.1404 ••• D+06 

o.o 

0.1212 ••• D+04 

0.1772 ••• D+04 

1538 1539 ••• 

•• 1378 1381 

Explanation 

Row and column identification number of the profile contained in this record: 

1, 1 represents row 1, column 1, in the DEM data set. 

Number of rows (elevations) and columns in this profile: 1201, 1 indicates 

there are 1201 elevations and 1 column in this profile. 

Translated to the decimal, -428400.0 and 1404000.0 are the ground planimetric 

coordinates (arc seconds) of the first elevation in the profile, thus -119 and 

39 degrees. 

Elevation of local datum for the profile. 

Minimum and maximum elevations for the profile. 

An array of m x n elevations (m=l201, n=l) for the profile expressed in units 

of measure of meters (record A, element 8, indicates meters as units of 

measure) • 
Figure 6.--Pre-eruption isometric plot of Mount St. Helens DEM. Generated 

from data obtained from July 15, 1979, photographs. View is 

from the northeast at a 45° altitude angle; vertical 

exaggeration is 3:1. 

17 
Figure ?.--Post-eruption isometric plot of Mount st. Helens DEM. Generated 

from data obtained from September 6, 1980, photographs. View 

is from the northeast at a 45° altitude angle; vertical 

exaggeration is 3:1. 

18 
APPENDIXES 
Data 

Element Contents 

1 File Name 

2 DEM Level Code 

3 Code defining N 

0 elevation pattern 

(regular or random) 

4 Code defining ground 

planimetric reference 

system 

5 Code defining 

zone in ground 

planimetric 

reference system 

APPENDIX A.--Digital Elevation Model Data Elements 

Logical Record Type A 

Type Ph~sical Record Format 

(FORTRAN ASCII BINARY Comment 

Notation) Format Format (B~tes) 

ALPHA Al44 144 

INTEGER*2 I6 2 Code l=DEM-1 

2=DEM-2 

3=DEM-3 

Normally set to Code 1 for 1:24,000-

scale DEM's and Code 3 for 

1:250,000-scale DEM's. 

INTEGER*2 I6 2 Code !=regular 

2=random 

Normally set to Code 1. 

INTEGER*2 I6 2 Code O,=Geographic 

l,=UTM 

2,=State Plane 

For codes 3-20, see Appendix G. 

Normally set to code 0 representing 

the geographic (latitude/longitude) 

system for 1:250,000-scale DEM's. 

Normally set to code 1 representing 

the UTM standard coordinate system 

for 1:24,000-scale DEM's. 

INTEGER*2 I6 2 Codes for State plane and UTM coordinate zones are given in Appendixes 

E and F for 1:24,000-scale DEM's. 

Code is set to zero for 1:250,000-

scale DEM's. 
tv 

~ 

Data 

Element 

6 

7 

8 

9 

10 

APPENDIX A.--Digital Elevation Model Data Elements 

Logical Record Type A--continued 

Contents 

Map projection 

parameters (see 

Appendix G) 

Code defining unit 

of measure for 

ground planimetric 

coordinates throughout the file 

Code defining unit 

of measure for 

elevation coordinates 

throughout the file 

Number (n) of sides 

in the polygon which 

defines the coverage 

of the DEM file 

Type 

(FORTRAN 

Notation) 

REAL*8 

INTEGER*2 

INTEGER*2 

INTEGER*2 

A 4,2 array containing REAL*8 

the ground coordinates 

of the four corners for 

the DEM 

Physical Record Format 

ASCII BINARY 

Format Format (Bytes) 

15D24.15 15 X 8 = 120 

I6 2 

I6 2 

I6 2 

4(2D24.15) 64 

Comment 

Definition of parameters for UTM 

projection is given in Appendix G. 

All 15 fields of this element are 

set to zero and should be ignored 

when geographic, UTM, or State 

plane coordinates are coded in data 

element 4. 

Code O,=Radians 

l,=feet 

2,=meters 

3,=arc-seconds 

Normally set to Code 2 for 1:24,000-

scale DEM's. Normally set to Code 

3 for 1:250,000-scale DEM's. 

Code l,=feet 

2,=meters 

Normally code 2 for meters for 

1:24,000-scale DEM's and 

1:250,000-scale DEM's. 

Usually n=4. 

The coordinates of the quadrangle 

.corners are ordered in a clockwise 

direction beginning with the 

southwest corner. The array is 

stored row-wise as pairs of 

eastings and northings. 
N 

N 

Data 

Element 

11 

12 

13 

14 

15 

APPENDIX A.--Digital Elevation Model Data Elements 

Logical Record Type A--continued 

Contents 

A two-element array 

containing minimum and 

maximum elevations for 

the DEM 

Type 

(FORTRAN 

Notation) 

REAL*8 

Counterclockwise angle REAL*8 

(in radians) from the 

primary axis of ground 

planimetric reference 

to the primary axis of 

the DEM local reference 

system 

Accuracy code for 

elevations 

A three-element array 

containing DEM spatial 

resolution (x,y,z). 

Units of measure for 

these resolution 

elements are consistent 

with those indicated 

by data elements 7 and 

8 in this record 

A two-element array 

containing the number 

of rows and columns 

(m, n) of profiles in 

the DEM 

INTEGER*2 

REAL*4 

INTEGER*2 

Physical Record Format 

ASCII BINARY 

Format Format (Bytes) 

2D24.15 16 

D24.15 8 

I6 2 

3El2.6 12 

2I6 4 

Comment 

The values are in the unit of 

measure given by data element 8 in 

this record. 

See figure 5. Normally set to zero 

to align with the coordinate system 

specified in element 4. 

Code O,=unknown accuracy 

!,=accuracy information is 

given in logical record type c. 

These elements are usually set to 

30, 30, 1 for 7.5-minute DEM's and 

3, 3, 1 for 1:250,000-scale DEM's. 

These units should not be confused 

with accuracy of the data. 

See figure 5. Normally the row 

value m is set to 1. Thus, the n 

value normally describes the number 

of columns in the DEM file. 
IV 

w 

Data 

Element 

1 

2 

3 

4 

APPENDIX B.--Digital Elevation Model Data Elements 

Logical Record Type B 

Contents 

A two-element array 

containing the row and 

column identification 

number of the DEM 

profile contained in 

this record 

A two-element array 

containing the number 

of rows and columns 

(m,n) of elevations in 

the DEM profile 

Type 

(FORTRAN 

Notation) 

INTEGER*2 

INTEGER*2 

A two-element array REAL*8 

containing the ground 

planimetric coordinates 

(Xg0 , Ygo> of the 

first elevation in the 

profile 

Elevation of local REAL*8 

datum for the profile. 

Physical Record Format 

ASCII BINARY 

Format Format (Bytes) 

2I6 4 

2I6 4 

2D24.15 16 

D24.15 8 

Comment 

See figure 5. The identification 

numbers range from 1 to m and 1 to 

n. Rows are normally set to 1 and 

should be disregarded. The column 

identification is the profile 

sequence number. 

see figure 5. This first element in 

the field corresponds to the number 

of nodes in this profile. The 

second element in this field is 

normally set to 1, specifying 1 

column per B record. 

See figure 5. 

The values are in the units of 

measure given by data element 8 in 

logical record type A. 
N 

~ 

Data 

Element 

5 

6 

APPENDIX B.--Digital Elevation Model Data Elements 

Logical Record Type B--continued 

Contents 

A two-element array of 

minimum and maximum 

elevations for the 

profile 

Type 

(FORTRAN 

Notation) 

REAL*8 

An array of m x n INTEGER*2 

elevations for the 

profile. Elevations are 

expressed in units of 

resolution elements 

Physical Record Format 

ASCII BINARY 

Format Format (Bytes) 

2D24.15 16 

mn(I6) 2mn 

Comment 

The values are in the unit of 

measure given by data element 8 in 

logical record type A. 

See data element 14 in Appendix A. 

A value in this array would be 

multiplied by the spatial resolution 

value and added to the elevation of 

the local elevation datum for the 

profile (data element 4 in this 

record) to obtain the elevation for 

the point. The planimetric ground 

coordinates of the point Xgp, Ygp, 

are computed according to the 

formulas in figure 5. 
N 

l11 

Data 

Element 

1 

2 

3 

4 

5 

6 

Contents 

Switch indicating 

availability of 

statistics in data 

element 2 

RMSE of file's datum 

relative to absolute 

datum (x,y,z) 

Sample size on which 

statistics in data 

element 2 are based 

Switch indicating 

availability of 

statistics in data 

element 5 

RMSE of DEM data 

relative to file's 

datum (x,y,z) 

Sample size on which 

statistics in datum 5 

are based 

APPENDIX C.--Digital Elevation Model Data Elements 

Logical Record Type c 

Type 

(FORTRAN 

Notation) 

INTEGER*2 

INTEGER*2 

INTEGER*3 

INTEGER*2 

INTEGER*2 

INTEGER*2 

Physical Record Format 

ASCII BINARY 

Format Format (Bytes) 

I6 2 

3I6 6 

I6 2 

I6 2 

3I6 6 

I6 2 

Comment 

Code l,=available 

O,=unavailable 

In same units as indicated by 

elements 7 and 8 of logical record 

type A record. 

If = 0 then accuracy will be assumed 

to be estimated rather than 

computed. 

Code 1,= available 

O,=unavailable 

In same units as indicated by 

elements 7 and 8 of logical record 

type A. 

If O, then accuracy will be assumed 

to be estimated rather than 

computed. 
APPENDIX D.--sample Quadrilateral Coordinates 

Geog:raEhic Coordinates UTM Coordinates 

Quad Corner 

No. Latitude Longitude Easting Northing 

1 35°30 1 107°37'30 11 261897.700 3931463.000 

2 35°37'30 11 107°37'30 11 262267.500 3945330.700 

3 35°37'30 11 107°30 1 273590.400 3945035.600 

4 35°30 1 107°30 1 273238.300 3931168.300 

26 
APPENDIX E.--Codes for State Plane Coordinate zones 

Alabama, East (AL) 

Alabama, West 

Alaska (AK) 

Arizona, East (AZ) 

Arizona, Central 

Arizona, West 

Arkansas, North (AR) 

Arkansas, South 

California (CA) 

0101 

0102 

5001 

thru 5010 

0201 

0203 

0202 

0301 

0302 

0401 

thru 0407 

Colorado, North (CO) 0501 

Colorado, Central 0502 

Colorado, south 0503 

Connecticut (CT) 0600 

Delaware (DE) 0700 

District of Columbia (DC) 1900 

Florida, North (FL) 0903 

Florida, East 0901 

Florida, West 0902 

Georgia, East (GA) 1001 

Georgia, West 1002 

Hawaii (HI) 5101 

thru 5105 

Idaho, East (ID) 1101 

Idaho, Central 1102 

Idaho, West 1103 

Illinois, East (IL) 1201 

Illinois, West 1202 

Indiana, East (IN) 1301 

Indiana, West 1303 

Iowa, North (IA) 1401 

Iowa, south 1402 

Kansas, North (KS) 1501 

Kansas, South 1502 

Kentucky, North (KY) 1601 

Kentucy, South 1602 

New York, West 3103 

New York, Long Island 3104 

North Carolina (NC) 3200 

North Dakota, North (ND) 3301 

North Dakota, south 3302 

Ohio, North (OH) 3401 

Ohio, South 3402 

Oklahoma, North (OK) 3501 

Oklahoma, south 3502 

Oregon, North (OR) 3601 

Oregon, South 3602 

Pennsylvania, North (PA) 3701 

Pennsylvania, south 3702 

Rhode Island (RI) 3800 

South Carolina, North(SC) 3901 

27 

Louisiana, North (LA) 

Louisiana, south 

Louisiana, Off Shore 

Maine, East (ME) 

Maine, west 

Maryland (MD) 

Massachusetts, Mainland (MA) 

Massachusetts, Island 

Michigan, East (MI) 

Michigan, Central 

Michigan, west 

Michigan, North (Lambert) 

Michigan, Central (Lambert) 

Michigan, South (Lambert) 

Minnesota, North (MN) 

Minnesota, Central 

Minnesota, south 

Mississippi, East (MS) 

Mississippi, west 

Missouri, East (MO) 

Missouri, Central 

Missouri, West 

Montana, North (MT) 

Montana, Central 

Montana, South 

Nebraska, North (NE) 

Nebraska, south 

Nevada, East (NV) 

Nevada, Central 

Nevada, west 

New Hampshire (NH) 

New Jersey (NH) 

New Mexico, East (NM) 

New Mexico, Central 

New Mexico, West 

New York, East (NY) 

New York, Central 

Utah, Central 

utah, south 

Vermont (VT) 

Virginia, North (VA) 

Virginia, south 

washington, North (WA) 

washington, south 

West Virginia, North (WV) 

West Virginia, south 

Wisconsin, North (WI) 

Wisconsin, Central 

Wisconsin, south 

Wyoming, zone I, East (WY) 

Wyoming, zone II, East 

Central 

1701 

1702 

1703 

1801 

1802 

1900 

2001 

2002 

2101 

2102 

2103 

2111 

2112 

2113 

2201 

2202 

2203 

2301 

2302 

2401 

2402 

2403 

2501 

2502 

2503 

2601 

2602 

2701 

2702 

2703 

2800 

2900 

3001 

3002 

3003 

3101 

3102 

4302 

4303 

4400 

4501 

4502 

4601 

4602 

4701 

4702 

4702 

4802 

4803 

4901 

4902 
APPENDIX E.--Codes for State Plane Coordinate zones--continued 

south carolina, south 3902 Wyoming, zone III, west 

South Dakota, North (SD) 4001 Central 4903 

South Dakota, south 4002 Puerto Rico (RQ) 5301 

Tennessee (TN) 4100 Virgin Islands, St. John, (VQ) 

Texas, North (TX) 4201 st. Thomas 5201 

Texas, North Central 4202 Virgin Islands, St. croix 5202 

Texas, Central 4203 American Samoa (AQ) 5300 

Texas, South Central 4204 Guam (GQ) 5400 

Texas, South 4205 

Utah, North (UT) 4301 

28 
APPENDIX F.--Universal Transverse Mercator zone Locations 

and Central Meridians 

zone C.M. Range Zone C.M. Range 

01 177W 180W-174W 31 003E OOOE-006E 

02 171W 174W-168W 32 009E 006E-012E 

03 165W 168W-162W 33 015E 012E-018E 

04 159W 162W-156W 34 021E 018E-024E 

05 153W 156W-150W 35 027E 024E-030E 

06 147W 150W-144W 36 033E 030E-036E 

07 141W 144W-138W 37 039E 036E-042E 

08 135W 138W-132W 38 045E 042E-048E 

09 129W 132W-126W 39 051E 048E-054E 

10 123W 126W-120W 40 057E 054E-060E 

11 117W 120W-114W 41 063E 060E-066E 

12 lllW 114W-108W 42 069E 066E-072E 

13 105W 108W-102W 43 075E 072E-078E 

14 099W 102W-096W 44 081E 078E-084E 

15 093W 096W-090W 45 087E 084E-090E 

16 087W 090W-084W 46 093E 090E-096E 

17 081W 084W-078W 47 099E 096E-102E 

18 075W 078W-072W 48 lOSE 102E-108E 

19 069W 072W-066W 49 lllE 108E-114E 

20 063W 066W-060W 50 117E 114E-120E 

21 057W 060W-054W 51 123E 120E-126E 

22 051W 054W-048W 52' 129E 126E-132E 

23 045W 048W-042W 53 135E 132E-138E 

24 039W 042W-036W 54 138E 138E-144E 

25 033W 036W-030W 55 147E 144E-150E 

26 027W 030W-024W 56 153E 150E-162E 

27 021W 024W-018W 57 159E 156E-162E 

28 015W 018W-012W 58 165E 162E-168E 

29 009W 012W-006W 59 171E 168E-174E 

30 003W 006W-OOOE 60 177E 174E-180W 

29 
w 

0 

APPENDIX G.--Parameters Required for Definition of Map Projections 

(00)* (01)** 

Parameter Geographic Universal 

(02) 

State 

Plane 

(03) 

Albers 

Conical 

Equal Area 

(04) 

Lambert 

Transverse Conformal 

Mercator (UTM) 

1 *** Longitude of any point 

within the zone 

2 *** Latitude of any point 

within the UTM zone 

3 *** *** 

4 *** *** 

5 *** *** 

6 *** *** 

7 *** *** 

8 *** *** 

9-15 

*** Semi-major axis of ellipsoid. If this field 

is left blank (=0), the value for Clarke's 1866 

spheroid in meters will be assumed. 

*** Eccentricity squared of ellipsoid (e2). 

*** 

*** 

*** 

*** 

*** 

*** 

If field is zero, this will indicate a sphere. 

If the field is >1, this field will be 

interpreted as containing the semi-minor axis 

of the ellipsoid. 

Latitude of 1st Standard Parallel 

Latitude of 2d Standard Parallel 

Longitude of Central Meridian 

Latitude of projection's origin 

False easting in the same units of measure as 

the semi-major axis of ellipsoid 

False northing in the same units of measure as 

the semi-major axis of ellipsoid 

(not used 

on this page) 

* 

** 

*** 

Note: 

Projection code number. 

For the Northern Hemisphere, supplying UTM zone will result in ignoring any given projection parameters. 

Parameter is not applicable to projection. 

All angles (latitudes, longitudes, or azimuth) are required in degrees, minutes, and arc-seconds in the 

packed real number format +DDDOMMOSS.sssss. 
w 

...... 

Parameter 

1 

2 

3 

4 

5 

6 

7 

8 

9 

10-15 

(not used 

on this page) 

APPENDIX G.--Parameters Required for Definition of Map Projections--continued 

(05) 

Mercator 

(06) 

Polar 

Stereographic 

Semi-major axis of ellipsoid. 

(07) 

Polyconic 

(08) 

Equidistant Conic 

Type A Type B 

If this field is left blank (=0), the value for Clarke's 1866 spheroid in meters will be assumed. 

Eccentricity squared of ellipsoid (e). 

If this is left blank (=0}, this will indicate a sphere. 

If the field is >1, this field will be interpreted as containing the semi-minor axis of the ellipsoid. 

*** 

*** 

Longitude 

of Central 

Meridian 

*** 

*** 

*** 

Longitude directed 

straight down below 

pole of map 

Latitude of true scale 

*** 

*** 

Latitude of 

Standard Parallel 

*** 

Latitude of 1st 

Standard Parallel 

Latitude of 2d 

Standard Parallel 

• • • • • • Longitude of Central Meridian • • • • • • • 

••• Latitude of projection's origin • 

• False easting in the same units of measure as the semi-major axis of ellipsoid • • • • • • • 

False northing in the same units of measure as the semi-major axis of ellipsoid ••••••• 

*** *** *** Zero Any non-zero number 
w 

N 

Parameter 

1 

2 

3 

4 

5 

6 

7 

8 

9-15 

(not used 

on this page) 

APPENDIX G.--Parameters Required for Definition of Map Projections--continued 

(09) 

Transverse 

Mercator 

Same as 

Projections 

03 thru 08 

Same as 

Projections 

03 thru 08 

Scale factor 

at Central 

Meridian 

*** 

Longitude of 

Central 

Meridian 

Latitude 

of origin 

(10) 

Stereographic 

(11) 

Lambert Azimuthal 

Equal-Area 

(12) 

Azimuthal 

Equidistant 

(13) 

Gnomonic 

• • • • • • • • • • • • Radius of the sphere of reference • 

*** *** 

*** *** 

*** *** 

If this field is left blank, the value 

6370997.0 meters will be assumed 

*** *** 

*** *** 

*** *** 

(14) 

Orthographic 

*** 

*** 

*** 

• • • • • • • • •• Longitude of center of projection • • • • • • • • • • • • 

• • • • • • • • • • • Latitude of center of projection • • • • • • • • • • • 

False easting in the same units of measure as the semi-major axis or radius of the sphere 

False northing in the same units of measure as the semi-major axis or radius of the sphere 
w 

w 

Parameter 

1 

2 

3 

4 

5 

6 

7 

8 

9-15 

(not used 

on this page) 

APPENDIX G.--Parameters Required for Definition of Map Projections--continued 

(15) 

General Vertical 

Near-Side Perspective 

(16) 

Sinusoidal 

(17) 

Equirectangular 

(Plate Caree) 

(18) (19) 

Miller Cylindrical Van Der Grinten I 

• • • • • • • • • • • • • • • • Radius of the sphere of reference • • • • • • • • • • • • • • • 

If this field is left blank, the value 

*** 

Height of perspective 

point above sphere 

*** 

Longitude of center of 

projection 

Latitude of center of 

projection 

6370997.0 meters will be assumed. 

*** *** *** *** 

*** *** *** *** 

*** *** *** *** 

• • • • • • • • • Longitude of Central Meridian • • • • • • • • • • • 

*** *** *** *** 

• False easting in the same units of measure as radius of the sphere • • • • • • • 

• False northing in the same units of measure as radius of the sphere •••••• 
Parameter 

1 

2 

3 

4 

w 

~ 

5 

6 

7 

8 

APPENDIX G.--Parameters Required for Definition of Map Projections--continued 

(20) 

Oblique Mercator 

(Definition Format A) (Definition Format B) 

Same as for projections 03 thru 09 

Same as for projections 03 thru 09 

Scale factor at the center of projection 

*** Angle of azimuth east 

of north for central 

line of projection 

*** Longitude of point 

along central line of 

projection at which 

angle of azimuth is 

measured 

Latitude of origin of projection 

Same as for projections 03 thru 19 

Same as for projections 03 thru 19 

Parameter 

(20) 

Oblique Mercator 

(Definition Format A) (Definition Format B) 

9 Longitude of first 

point defining central 

geodetic line of 

projection 

10 Latitude of first 

point defining central 

geodetic line of 

projection 

11 Longitude of second 

point defining central 

geodetic line of 

projection 

12 Latitude of second 

point defining central 

geodetic line of 

projection 

13 Zero 

14 and 15 

(not used for this 

projection) 

*** 

*** 

*** 

*** 

Any non-zero 

number 
APPENDIX H.--Digital Terrain Tapes 

Contents 

Introduction •••••••••••••••••••••••••••••••••••••••••• 

Characteristics 

Data production 

Accuracy •••••••••••••••••••••••••••••••••••••••••••••• 

Data records •••••••••••••••••••••••••••••••••••••••••• 

Tables 

Table Hl. Type A logical record data content for a 

digital terrain tape ••••••••••••••••••••• 

H2. Type B logical record data content for a 

digital terrain tape ••••••••••••••••••••• 

H3. Type c logical record data content for a 

digital terrain tape •••••••••••••••••••• 

35 

Page 

36 

36 

36 

37 

37 

Page 

38 

39 

40 
DIGITAL TERRAIN TAPES 

Introduction 

Digital terrain tapes are a type of 

digital elevation data produced by the 

DMA and distributed by USGS. Each 

digital terrain tape file corresponds in 

coverage to a 1° x 1° block (one-half of 

a standard 1:250,000-scale 1° x 2° quadrangle). Digital terrain tapes are 

available for the conterminous United 

States and Hawaii. The data are distributed by USGS as produced by the DMA 

and, as such, they do not conform to the 

standard USGS DEM tape format. 

Characteristics 

A 1:250,000-scale 

tape file has 

digital terrain 

the following 

characteristics: 

• The data consist of a regular array 

of elevations referenced in 

digitizer coordinates at increments 

of 0.01 inch. 

• The unit of coverage is a 1 o 

block representing one half 

1:250,000-scale 1° x 2° map. 

• The positions of the four corners 

of the 1° x 1° block are stated in 

digitizer and geographic (latitude/ 

longitude) coordinates. 

• The data are ordered from south to 

north in profiles that are ordered 

from west to east. 

• The data are stored as profiles in 

which the spacing of elevations 

along and between each profile is 

0.01 inch (approximately 200 feet 

at the source map scale of 

1:250,000). 

Data Production 

Digital terrain tapes were produced 

as a byproduct of the production of 

three-dimensional relief maps. Production began in the early 1960's with the 

36 

development of the Digital Graphics 

Recorder (DGR) system. The DGR system 

consisted of manual line-following digitizer connected to a computer system; it 

was capable of recording digital elevation data by tracing contour lines etched 

on metal plates. Digital traces of 

ridges and streams were added to the 

digital contour data and an interpolation algorithm was applied to produce a 

cartesian grid of elevation values spaced 

at 0.01 inch intervals. The gridded 

elevation data were then employed as a 

digital template to control a tool for 

carving the plaster forms used to mold 

raised-relief maps. 

Although the DGR system was initially 

developed solely to automate the production of raised-relief maps, the versatility of the gridded digital elevation 

data was quickly recognized, and the 

concept of a 1:250,000- scale digital 

elevation data base was born. As the 

demand for the digital terrain tapes 

increased, the data collection and 

processing techniques were refined and 

streamlined, and the DGR system was 

eventually replaced by the Automated 

Graphic Digitizing System (AGDS). The 

AGDS is an automated scanning system that 

digitizes data along regularly spaced 

scan-lines. For production of digital 

terrain tapes, stable base materials 

containing contour lines and ridge and 

stream traces, as depicted on 1:250,000-

scale topographic maps, were digitized 

on the AGDS. The data were then vectorized, tagged, and edited using an interactive digitizing station. An interpolation algorithm was subsequently applied 

to produce the cartesian grid of elevation values at 0.01 inch intervals. 

The 1:250,000-scale digital terrain 

tape data base was completed for the 

conterminious United States and Hawaii 

in the late 1970's. Since that time, 

1:250,000-scale DEM's (described on page 

4) have been completed for nearly all of 

the area covered by the digital terrain 

tapes. In addition, 1:250,000-scale DEM 

data is available for most of Alaska 

where digital terrain tapes were never 

produced. Because the 1:250,000-scale 

DEM's are more rigorously checked for 

accuracy and consistency, they are 

generally considered the preferable 
source of digital elevation data at this 

scale. The digital terrain tapes, 

however, remain a valuable resource and 

will continue to be distributed by USGS. 

Accuracy 

The accuracy of the digital terrain 

tapes is compatible with the accuracy of 

the stable-base 1:250,000-scale map 

sheets from which they were digitized. 

Neither the maps nor the tapes have been 

completely tested for vertical accuracy. 

Data Records 

Digital terrain tape data are 

distributed by the USGS on multifile 

nine-track magnetic tape, usually in odd 

parity at 1,600 bpi. Each data file 

represents elevations for a planimetric 

grid of points covering part (usually 

one-half) of a 1:250,000-scale map sheet. 

Within each file, data are arranged 

in sequential logical records. Three 

types of logical record formats are used: 

37 

Type A logical record--The first 

logical record in a digital terrain 

tape file is a type A record. It 

contains general information about 

the digital model. Figure Hl 

depicts the layout of the 78 bytes 

which constitute the record and 

provides a description of each data 

field in the record. Unless 

otherwise specified, all data fields 

represent binary integer numbers. 

Type B logical record--The type B 

record is a variable length record 

which contains elevation profile 

data. Figure H2 depicts the layout 

of this variable length record and 

provides a description of each data 

field. 

Type c logical record--The type C 

record is the last logical record in 

a digital terrain tape file and 

describes the number of profiles in 

the file. Figure H3 depicts the 

layout of the record's 12 bytes, and 

provides a description of each data 

field. 
Table Hl.--Type A logical record data content for a 

digital terrain tape 

Byte Content 

1-12 ............ Sheet number (EBCDIC) 

13-18 ............ Map series (EBCDIC) 

19-24 ............ Map edition (EBCDIC) 

25-26 ............ Map projection code number, code 

1 is for UTM projection 

27-28 ............ Map projection zone number 

29-30 ............ Code number for elevation-data units 

=0 for meters 

=1 for feet 

31-32 ............ x-coordinate of southwest map corner! 

33-34 ............ y-coordinate of southwest map corner 

35-36 ............ x-coordinate of northwest map corner 

37-38 ............ y-coordinate of northwest map corner 

39-40 ............ x-coordinate of northeast map corner 

41-42 ............ y-coordinate of northeast map corner 

43-44 ............ x-coordinate of southeast map corner 

45-46 ............ y-coordinate of southeast map corner 

47-50 ............ Longitude of southwest map corner2 

51-54 ............ Latitude of southwest map corner 

55-58 ............ Longitude of northwest map corner 

59-62 ............ Latitude of northwest map corner 

63-66 ............ Longitude of northeast map corner 

67-70 ............ Latitude of northeast map corner 

71-74 ............ Longitude of southeast map corner 

75-78 ............ Latitude of southeast map corner 

1All x and y coordinates are in 0.01-inch units. 

2All longitudes and latitudes are in arc-second units. 

38 
Table H2.--Type B logical record data content for a 

digital terrain tape 

Byte content 

1-2 •••••••••• Map x-coordinate of the first point in the 

profile (x0 ) in one-hundredths of an inch 

3-4 •••••••••• Map y-coordinate of the first point in the 

profile (y0 ) in one-hundredths of an inch 

5-6 •••••••••• x-component of map step between profile 

elevation points (x) in one-hundredths of 

an inch (always equals 0) 

7-8 •••••••••• y-component of map step between profile 

elevation points (y) in one-hundredths of 

an inch (always equals 1) 

9-10 •••••••• Number of elevation points (m) in the profile 

11-12 Elevation of first profile point (H1 ) 

13-14 Elevation of second profile point (H2) 

(2m+9) - (2m+l0) ••• Elevation of mth profile point (Hm> 

39 
Table H3.--Type C logical record data content for a 

digital terrain tape 

Byte Content 

1-2 A string of 16 '1' 

3-4 ........................... A string of 16 '1' 

5-6 A string of 16 '1' 

7-8 A string of 16 '1' 

9-10 ........................... The number 1 

11-12 Number of profiles 

(type B logical 

records) in the 

bits 

bits 

bits 

bits 

digital terrain file 

40 



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