**Evaluation of Techniques to Determine Landscape Areas**

December 1998

Prepared For:

United States Bureau of Reclamation

Grant Agreement #8-FG-20-16810

Prepared By:

Irrigation Training and Research Center

BioResource and Agricultural Engineering Department

California Polytechnic State University

San Luis Obispo, CA 93407

Phone: 805-756-2434

FAX: 805-756-2433

# Executive Summary

**Introduction**

Implementing Best Management Practices includes improving landscape
irrigation performance and developing landscape water budgets. Water
budgeting requires knowledge of landscape areas. Methods for measuring
landscape areas range from pacing an area to interpreting aerial
photographs. Each method varies in its ease of use, cost, and associated
errors. Consequently, the application of each method will vary depending
on the requirements and limitations of each individual agency.

**Measurement Technology**

Methods for measuring landscape areas were divided into two broad
categories: field based and image based. Field based methods involve
taking measurements on site and include pacing, odometer wheel, optical
rangefinder, stadia, taping, electronic distance measurement, compass,
\" total station \" surveying, and global positioning system (GPS).

Image based methods use some form of photography for the analysis.
Aerial photographs may be available from municipal or county agencies.
Recently, one meter per pixel orthophotographs have become available on
the Internet at no cost. Areas can be determined directly by a
technician by counting squares, using geometric shapes method, or using
a planimeter. If the images are in digital format on the computer,
software can be used to make area calculations. Image based techniques
vary in the equipment and the technical expertise required.

**Procedures**

The Irrigation Training and Research Center (ITRC) at Cal Poly San Luis
Obispo evaluated several field and image based methods of area
measurement. The evaluation consisted of measuring landscape areas of
three parks in San Luis Obispo, California: Santa Rosa, French, and
Mitchell Parks. These parks were selected to represent a wide range in
landscape area, plant size and density. Each park was measured using the
field and image based methods listed in Table ES-1 below.

Table ES-1. Description of methods used for area measurement evaluation.

+-----------------------------------+-----------------------------------+
| **Field Based Technique**         | **Image Based Technique**         |
+-----------------------------------+-----------------------------------+
| 1\. Global positioning system     | 1\. Digital maps with ArcView^®^  |
|                                   | software                          |
+-----------------------------------+-----------------------------------+
| > 1a. one centimeter accuracy     | > 1a. one foot per pixel map      |
+-----------------------------------+-----------------------------------+
| > 1b. one meter accuracy          | > 1b. one meter per pixel map     |
+-----------------------------------+-----------------------------------+
| 2\. Compass and odometer wheel    | 2\. Hard copy map with planimeter |
+-----------------------------------+-----------------------------------+
| 3\. Laser rangefinder             | > 2a. one foot per pixel map      |
+-----------------------------------+-----------------------------------+
|                                   | > 2b. one meter per pixel map     |
+-----------------------------------+-----------------------------------+

The results from the one centimeter GPS method were used to establish a
"standard area" and the results from the other methods were compared to
the standard.

**Results**

All of the methods evaluated resulted in measurements of the entire park
area within 7% of the standard or reference value (Table ES-2). When
sub-area measurements were compared, errors ranged from 0 to 36% (Table
ES-3). The larger errors were associated with extremely small areas
using the image-based planimeter method.

Table ES-2. Comparison of area measurements for each method.

  ---------- --------------- ------- --------- ------------ --------- -------------- ---------
             Reference Area  Field             Image Based                           
             (ft^2^)         Based                                                   

  Park       (Determined by  GPS (1  Wheel and ArcView^®^             Planimeter\*   
                             m)                                                      

             1 cm GPS)               Compass   1 ft/pixel   1 m/pixel 1 ft/pixel     1 m/pixel

  French     320,000         -0.2%   2.5%      -0.3%        -0.1%     -4.6%          -4.7%

  Mitchell   91,300          -1.4%   0.8%      6.8%         6.2%      4.1%           6.2%

  Santa Rosa 229,860         -1.2%   -0.4%     1.0%         -3.0%     1.4%           1.0%
  ---------- --------------- ------- --------- ------------ --------- -------------- ---------

\* The 1 m/pixel aerial photographs taken from the Internet were missing
a portion of French Park. The reference area was adjusted for the
methods using this aerial photograph.

Table ES-3. Percent error for each measurement method and each

> sub-area for Santa Rosa Park.

  ----------- --------- -------- -------------- ------- --------- ------- ------------ -------- --------- -------
  Reference   Field              Image Based                                                              
              Based                                                                                       

  GPS         Wheel and          Computer                                 Planimeter                      
              Compass            Software                                                                 
                                 (ArcView^®^)                                                             

                                 1 ft/pixel             1 m/pixel         1 ft/pixel            1 m/pixel 
                                 photo                  photo             photo                 photo     

  ft^2^       ft^2^     \% Error ft^2^          \%      ft^2^     \%      ft^2^        \% Error ft^2^     \%
                                                Error             Error                                   Error

  36          39        -8.3%    43             19.4%   \*        \*      \*           \*       \*        \*

  60          60        0.0%     65             8.3%    \*        \*      82           36.7%    \*        \*

  98          108       -10.2%   97             -1.0%   \*        \*      \*           \*       \*        \*

  192         220       -14.6%   180            -4.7%   \*        \*      \*           \*       \*        \*

  303         224       26.1%    280            -7.6%   \*        \*      230          -24.1%   \*        \*

  935         950       -1.6%    880            -5.6%   \*        \*      810          -13.4%   \*        \*

  1868        1880      -0.6%    1830           -2.0%   \*        \*      1630         -12.7%   \*        \*

  4030        3990      1.0%     3700           -8.1%   \*        \*      3600         -10.7%   \*        \*

  72800       70600     3.0%     75200          3.3%    75200     3.3%    76000        4.4%     68000     -6.6%

  73800       73000     1.1%     73600          -0.3%   69100     -6.3%   75000        1.6%     78300     6.1%

  75700       78000     -3.0%    75900          0.2%    73600     -2.7%   76000        0.4%     70600     -6.7%
  ----------- --------- -------- -------------- ------- --------- ------- ------------ -------- --------- -------

\* Because of the limited visibility in the aerial photographs not all
of the smaller individual\
sub-areas could be obtained.

**Discussion**

Field based techniques were more consistent than image based techniques
and provided results with errors less than 2.5%. Both the high-tech (GPS
and laser rangefinder) and low-tech (compass and odometer wheel) methods
yielded relatively accurate results, although the costs and skill level
vary for the different methods. The extent of measurements necessary and
the resources available will determine if any of these methods are
appropriate. In some cases, hiring a consultant to make the required
measurements may be the preferred option.

Image based techniques require the least amount of surveying knowledge.
Many agencies have access to orthophotos, planimeters or software needed
for analyzing images. The planimeter method yielded the highest errors.
However, the 7% error resulting from using this approach would be more
than acceptable in many agencies. Other errors associated with image
based techniques involve difficulties in boundary identification. Site
visits are usually necessary in all but extremely new parks.

**Conclusions**

When selecting a method for area measurement, the agency must balance
issues of cost versus accuracy. In addition, they must consider the
nature of site, availability of images and equipment, technical
expertise of staff, and time resources available. Table ES-4 gives a
comparison of costs associated with each method.

Table ES-4. Labor Cost comparisons for various area measurement
techniques.

  ---------------------------------------------------------------------------------------
  Park       Technique          Time                Total   Cost      Total   
                                Required            Time              Cost    
                                (hrs)                                         
  ---------- ------------------ ---------- -------- ------- --------- ------- -----------
                                Field      Office   (hrs)   (\$/hr)   (\$)    (\$/acre)

  French     GPS 1M Accuracy    5          2        7       20        140     14

  (337,500   Compass & Wheel    10         2        12      20        240     25
  ft^2^)                                                                      

             Orthophoto &       1.0        1        2       20        40      4
             ArcView^®^                                                       

             Orthophoto &       1.5        1        2.5     20        50      5
             Planimeter                                                       

  Mitchell   GPS 1M Accuracy    4          1        5       20        100     29

  (91,300    Compass & Wheel    10         2        12      20        240     71
  ft^2^)                                                                      

             Orthophoto &       1.0        1        2.0     20        40      12
             ArcView^®^                                                       

             Orthophoto &       1          1.5      2.5     20        50      15
             Planimeter                                                       

  Santa Rosa GPS 1M Accuracy    4          2        6       20        120     15

  (229,860   Compass & Wheel    12         2        14      20        280     34
  ft^2^)                                                                      

             Orthophoto &       1.0        1        2.0     20        40      5
             ArcView^®^                                                       

             Orthophoto &       1          1.5      2.5     20        50      6
             Planimeter                                                       
  ---------------------------------------------------------------------------------------

Every effort should be made to ensure that the larger sub-areas are
measured as accurately as possible. Smaller sub-areas measured with less
accurate methods will have little affect on the final results. It is
also important to have a method to check measurements, either with other
maps or summing areas.

**Recommendations**

In order to facilitate agencies in completing landscape area
measurements for implementing water budgets, several programs would be
appropriate:

-   Education regarding the issues associated with area measurement

-   Training on various area measurement techniques

-   Equipment pool for cooperating agencies to utilize

-   Technical support for cooperating agencies with specific area
    measurement questions

# Table of Contents

Executive Summary ES-1

List of Tables [iii](#list-of-tables)

List of Figures [iv](#list-of-figures)

I. Introduction [1](#i.-introduction)

II\. Measurement Technology [2](#ii.-measurement-technology)

A. Field Techniques [2](#a.-field-techniques)

1\. Pacing [2](#pacing)

2\. Odometer [3](#odometer)

3\. Optical Rangefinder [3](#optical-rangefinder)

4\. Stadia [3](#stadia)

5\. Taping [4](#taping)

6\. Electronic Distance Measurement (EDM)
[4](#electronic-distance-measurement-edm)

7\. Compass [5](#compass)

8\. Global Positioning System [6](#global-positioning-system)

9\. Total Station [6](#total-station)

B. Photograph and Computer Image Issues
[7](#b.-photograph-and-computer-image-issues)

1\. Aerial Photographs [7](#aerial-photographs)

2\. Digitalization [8](#digitalization)

3\. On-Line Aerial Orthophotos [8](#on-line-aerial-orthophotos)

C. Photograph and Computer Image Techniques
[9](#c.-photograph-and-computer-image-techniques)

1\. Counting Squares [9](#counting-squares)

2\. Geometric Shapes [9](#geometric-shapes)

3\. Planimeter [10](#planimeter)

4\. Computer Software [10](#computer-software)

III\. Procedures [12](#iii.-procedures)

A. Sites [12](#a.-sites)

B. Reference Area Measurements [13](#b.-reference-area-measurements)

C. Field Measurements [13](#c.-field-measurements)

1\. Global Positioning System [13](#global-positioning-system-1)

2\. Compass and Odometer Wheel [14](#compass-and-odometer-wheel)

3\. Laser Rangefinder [14](#laser-rangefinder)

D. Image Based Measurements [14](#d.-image-based-measurements)

1\. Computer Software [14](#computer-software-1)

2\. Planimeter [14](#planimeter-1)

IV\. Results [15](#iv.-results)

V. Discussion [17](#v.-discussion)

A. Reference Measurements [17](#a.-reference-measurements)

B. Comparison of Techniques [18](#b.-comparison-of-techniques)

1\. Field Based [20](#field-based)

2\. Image Based [20](#image-based)

C. General Measurement Issues [21](#c.-general-measurement-issues)

1\. Size of Landscape Areas [21](#size-of-landscape-areas)

2\. Confidence in Data [22](#confidence-in-data)

3\. Costs and Resource Availability
[22](#costs-and-resource-availability)

VI\. Conclusions [23](#vi.-conclusions)

Choosing a Method [23](#choosing-a-method)

Approach and Process [23](#approach-and-process)

VII\. Recommendations [25](#vii.-recommendations)

VIII\. Glossary [26](#viii.-glossary)

IX\. References [28](#ix.-references)

Appendix A Fundamentals of Area Determination

Appendix B Accuracy and Error in Measurement

Appendix C Procedures for downloading photographs and using ARCVIEW^®^

Appendix D California Conservation Corps

Appendix E Equipment Manufacturers

Appendix F Water District Resources for Area Measurement

Appendix G Assessment Tool for measurement technique selection

# List of Tables

Table 1. Landscape areas of French, Mitchell, and Santa Rosa Parks
measured with 1 cm GPS. [12](#__RefHeading___Toc438353517)

Table 2. Comparison of area measurements for each method.
[15](#__RefHeading___Toc438353518)

Table 3. Percent error for each measurement method for Santa Rosa Park.
[15](#__RefHeading___Toc438353519)

Table 4. Landscape areas determined with a laser rangefinder.
[16](#__RefHeading___Toc438353520)

Table 5. Labor costs associated with determining landscaped areas in
parks. [16](#__RefHeading___Toc438353521)

Table 6. Equivalent professional surveyor costs for area measurement in
this study. [18](#__RefHeading___Toc438353522)

Table 7. Summary of costs and constraints for area determination
methods. [19](#__RefHeading___Toc438353523)

Table 8. Santa Rosa Park errors considering only the largest landscape
areas\...\...\...\...\..... 22

# List of Figures

Figure 1. Pacing to determine length of a line.
[2](#__RefHeading___Toc438353530)

Figure 2. Odometer wheel to measure length of a line.
[3](#__RefHeading___Toc438353531)

Figure 3. Measuring distance by stadia.
[3](#__RefHeading___Toc438353532)

Figure 4. Measuring distance using a steel tape.
[4](#__RefHeading___Toc438353533)

Figure 5. Electronic distance measurement (EDM) instrument.
[4](#__RefHeading___Toc438353534)

Figure 6. A hand held laser rangefinder.
[5](#__RefHeading___Toc438353535)

Figure 7. Staff compass. [5](#__RefHeading___Toc438353536)

Figure 8. GPS equipment by Trimble. [6](#__RefHeading___Toc438353537)

Figure 9. Automatic total station and electronic field book.
[7](#__RefHeading___Toc438353538)

Figure 10. Santa Rosa Park image from City of San Luis Obispo images
(resolution = 1 ft/pixel). [8](#__RefHeading___Toc438353539)

Figure 11. Santa Rosa Park image from Microsoft TerraServer website
(resolution = 1 m/pixel). [9](#__RefHeading___Toc438353540)

Figure 12. Planimeter for area determination from printed
orthophotographs. [10](#__RefHeading___Toc438353541)

Figure 13. Orthophotograph of Santa Rosa Park inserted as a theme in
ArcView^®^. [11](#__RefHeading___Toc438353542)

Figure 14. CCC members using a Trimble ProXL^®^ for GPS readings.
[13](#__RefHeading___Toc438353543)

# I. Introduction

California's population has increased approximately 35% over the last
ten years, reaching 32.6 million people in 1995. It is estimated that
the population will reach 47.5 million by the year 2020, thus increasing
the state's demand for water. During an average year, the gap between
the state's water demands and supplies will be 2.9 MAF by 2020.

Improving the efficiency with which we use our limited water supplies is
one strategy to mitigate the effects of California's increasing demand
for water. Specifically, Best Management Practices (BMP's) emphasize
improving landscape irrigation performance and developing landscape
water budgets.

Water budgeting requires knowledge of the irrigated landscape area. One
high-technology approach uses aerial photography and computer aided
analysis for area measurements. This method requires field measurements
to validate results. In other cases, area measurements are completed
using tape measures and measuring wheels.

The aerial photography approach may be a cost-effective method for
large-scale projects, but the approach may be too expensive for smaller
areas. Consequently, there is a need to identify and evaluate methods,
techniques, and equipment for area measurement, which would be
appropriate for smaller projects. Developing easy and economically
feasible procedures to estimate landscape areas will enable smaller
communities to obtain the data needed to implement "Water Budgets" as
part of the BMP's.

# II. Measurement Technology

Computing landscape and hardscape areas may require the measurement of
lines (lengths and angles) forming the boundary of an area by using one
or more of the following technologies. They can be divided into two
categories: those using field measurements and those using photograph or
image measurements.

*Field Techniques‑*

-   Pacing, length

-   Odometer Wheel, length

-   Optical Rangefinder, length

-   Stadia, length, horizontal angle

-   Taping, length

-   Electronic Distance Measurement (EDM), length

-   Compass, angle

-   Global Positioning System (GPS), position

-   Total Station, length, angle

*Photograph and Computer Image Techniques‑*

-   Counting squares

-   Geometric shapes

-   Planimeter, area

-   Computer Software, area

## A. Field Techniques

The following field techniques measure distances between points. They
are listed in order of least to most accurate. Appendix E contains
additional information regarding equipment and their manufacturers.

### 1. Pacing

Pacing consists of counting the number of steps between two points
(Figure 1). The length of an individual's pace is determined by walking
a known length (100 -- 300 ft) and dividing the distance by the number
of steps taken. Pacing can be used to check measurements made by other
methods. It requires no equipment and little training. The accuracy of
the method is between one foot in 100 ft (1/50 - 1/100) of measurement,
depending on the person\'s skill. Appendix B discusses the impact of
errors in measuring distances on area computation.

![](media/image1.png){width="1.4541666666666666in"
height="1.2402777777777778in"}

[]{#__RefHeading___Toc438353530 .anchor}Figure 1. Pacing to determine
length of a line.

### 2. Odometer

An odometer is a wheel rolled between two points. The distance is
calculated by multiplying the number of revolutions by the wheel\'s
circumference. The smoother the path the wheel travels, the more
accurate the measurement. This method is particularly useful for curved
lines. Odometer wheels can also be used to verify other measurements.
The accuracy of the method is approximately 1/200.

![](media/image2.png)

[]{#__RefHeading___Toc438353531 .anchor}Figure 2. Odometer wheel to
measure length of a line.

### 3. Optical Rangefinder

An optical rangefinder uses the focusing of lenses on a distant object
to estimate the distance to the object. This technique is the same as
single-reflex lens cameras. Rangefinders have a maximum range of 150 ft
and an accuracy of 1/50.

### 4. Stadia

Stadia measurements use a surveying transit telescope. There are three
horizontal lines crossing the vertical line in the middle of the
telescope. The distance measured is proportional to the difference
between the top and bottom rod readings. Stadia accuracy can reach
1/500.

[]{#__RefHeading___Toc438353532
.anchor}![](media/image3.wmf){width="3.0597222222222222in"
height="1.8916666666666666in"}Figure 3. Measuring distance by stadia.

### 5. Taping

Tape measures can be used for most small and medium distances (Figure
4). The most common tape length is 100 ft, although longer tape lengths
are also available. Plumb bobs are used to make horizontal measurements
over rough and sloped terrain. Taping accuracy range from 1/100
to1/5000. The accuracy attained will depend on the skill and attention
to detail of personnel using the tape.

![](media/image4.jpeg){width="2.826388888888889in"
height="2.1333333333333333in"}

[]{#__RefHeading___Toc438353533 .anchor}Figure 4. Measuring distance
using a steel tape.

### 6. Electronic Distance Measurement (EDM)

EDM is usually integrated into a *total station.* EDM emits a directed
signal to a reflector located at the end point of a line. The signal is
reflected back to the EDM, and the length of a line is determined
(Figure 5). Distance measurements of several miles are possible.
Accuracy of 1/1,000,000 is obtainable. The shorter the distance, the
greater the error.

![](media/image5.png){width="3.2944444444444443in"
height="2.597916666666667in"}

[]{#__RefHeading___Toc438353534 .anchor}Figure 5. Electronic distance
measurement (EDM) instrument.

A laser rangefinder is a hand held version of the EDM (Figure 6). The
basic instruments measure up to 2400 ft with accuracy ranging from 3 to
9 ft. Advanced instruments measure up to 32,000 ft with an accuracy from
0.15 to 0.60 ft. The laser rangefinders can be used with or without
prism reflectors. Several models of the laser rangefinder also include
an inclinometer (±0.1 degree accuracy) and compass (±0.3 degree
accuracy), extending their capabilities to include slope and horizontal
angle measurements.

![](media/image6.png){width="2.6958333333333333in" height="2.3875in"}

[]{#__RefHeading___Toc438353535 .anchor}Figure 6. A hand held laser
rangefinder.

### 7. Compass

A compass uses a magnetic needle to indicate a line\'s direction
referenced from magnetic north (Figure 7). If the line must be related
to other maps, the magnetic reading are converted *to true north* values
by applying the magnetic declination for the area. Magnetic declination
represents the difference between magnetic north and true north. The
magnetic declination varies by location and time. Quality compasses can
be read to the nearest degree (estimate 1/2 degree). Any metal
object---chain link fence, light pole, and power lines---affects the
reading from the compass.

![](media/image7.jpeg){width="3.057638888888889in"
height="2.2930555555555556in"}

[]{#__RefHeading___Toc438353536 .anchor}Figure 7. Staff compass.

### 8. Global Positioning System

Global Positioning System (GPS) represents a satellite-based surveying
and navigation system. The system consists of a network of 24 satellites
circling the earth with an altitude of 12,500 miles. The network was
created and controlled by the US military. Civilian uses of the network
are expanding, and it is becoming a significant resource for determining
location. A GPS *receiver* uses the signal from four or more satellites
to determine its position on or above the earth (Figure 8). Due to
military interests, the signal being sent by the satellites is
constantly being altered such that accuracy is limited to ± 100 m.

The measurement\'s accuracy using satellite systems may be increased in
one of two ways:

1.  Correcting the measurements taken with data from the military
    indicating the amount of error in the signal (*post processing*
    correction)

2.  Correcting the measurement by placing a second receiver at a known
    location and computing the distance and direction from the known
    position to the new position (*differential* correction)

Differential correction can be done either in post processing or real
time. Real time correction requires both receivers to have radio
communication with each other. Depending on the receiver's design,
measurements can be as accurate as ± 1 cm horizontally and ± 2 cm
vertically. The output from the receiver is a point location---x, y, z
coordinates---in either a known map coordinate system or in a local grid
system.

![](media/image8.png){width="1.6791666666666667in" height="3.41875in"}

[]{#__RefHeading___Toc438353537 .anchor}Figure 8. GPS equipment by
Trimble.

### 9. Total Station

A "total station" has a theodolite, for horizontal and vertical angle
measurement, and an EDM for electronic distance measurement (Figure 9).
This instrument is the heart of a professional surveyor's
instrumentation. A *manual* total station uses manual reading of angles
and is entered into a field book. An *automatic* total station reads and
enters angles and distances into an electronic field book computer with
the touch of a button. Most instruments used today read angles to 5
seconds of a degree or better.

![](media/image9.png){width="1.8333333333333333in"
height="3.198611111111111in"}

[]{#__RefHeading___Toc438353538 .anchor}Figure 9. Automatic total
station and electronic field book.

## B. Photograph and Computer Image Issues

Aerial photographs are available for many parts of California.
Orthophotographs created by the United States Geological Survey (USGS)
and maps created for construction projects are often available for a
small fee. Aerial photographs may be available as a print or a digital
image.

Districts interested in using aerial photographs should consider two
questions:

What type of photograph is available from other agencies within their
city or county?

What type of equipment and software are available to determine landscape
areas from the photographs?

### 1. Aerial Photographs

Two important qualities of aerial photographs include the *uniformity of
scale* and the *actual scale* of the photograph. Aerial photographs are
a perspective view, in which the image is viewed from a single point.
Therefore, measurements taken directly from a photograph may be
inaccurate. The greater the changes in elevation across the photograph
and the closer to the edge of the photograph the measurement is taken,
the greater the error. Errors up to 15% are possible. For aerial
photographs to be useful in map work, the scale of the photograph must
be constant across the entire photograph.

Uniform scale is accomplished by creating an *orthophoto* from multiple
images of a given area. "Orthophotos combine the image characteristics
of a photograph with the geometric qualities of a map. They serve a
variety of purposes, from interim maps to field references for Earth
science investigations and analyses. The digital orthophoto is useful as
a layer of a geographic information system (GIS) and as a tool for
revision of digital line graphs and topographic maps\" (USGS, 1998).

"Unlike a standard aerial photograph, relief displacement in orthophotos
has been removed so that ground features are displayed in their true
ground position. This allows for the direct measurement of horizontal
distance, areas, angles, and positions\" (USGS, 1998).

### 2. Digitalization

The scale of commonly used photographs ranges from 1\" = 100 ft to 1\" =
20,000 ft. Photographs to be used by computers must first be scanned and
digitized to create computer images. Software (i.e., SocketSet^®^) is
used to create orthophotos from photographs. The digital
orthophotographs are represented as a collection of points.
Digitalization fixes the resolution of the image, and the computer image
consists of a number of pixels (dots) on the screen. Aerial photographs
taken for planning or construction purposes will most likely have a
resolution of one or two feet per pixel (i.e., every pixel on the screen
represents one or two feet on the ground). Smaller scale images may have
a resolution up to 100 ft per pixel. Obviously, the better the
resolution (fewer feet per pixel), the more detail that can be detected
in the image (Figure 10).

![](media/image10.png){width="3.9069444444444446in"
height="2.7958333333333334in"}

[]{#__RefHeading___Toc438353539 .anchor}Figure 10. Santa Rosa Park image
from City of San Luis Obispo images (resolution = 1 ft/pixel).

### 3. On-Line Aerial Orthophotos

Another source of aerial orthophotographs is through a free service
provided by Microsoft. On June 24, 1998, Microsoft began placing digital
aerial photographs on the Internet website
<http://terraserver.microsoft.com/default.htm>. This site allows users
to download aerial photographs in digital form (digital orthorphoto
quadrangles). The scale of these images is 1\" = 2,000 ft and the
resolution is 3 ft/pixel. Aerial photographs of most cities in
California can be found on this site (Figure 11), and Microsoft is
constantly adding images to the web site. The images can be downloaded
for **free**. Downloading the images requires Internet Explorer 4.0 or
Netscape 4.0 or newer versions. Appendix C contains complete
instructions on downloading 3 ft/pixel images from the Microsoft
Terraserver website.

![](media/image11.wmf){width="4.029861111111111in"
height="2.6868055555555554in"}

[]{#__RefHeading___Toc438353540
.anchor}![](media/image12.wmf){width="4.029861111111111in"
height="2.6868055555555554in"}Figure 11. Santa Rosa Park image from
Microsoft TerraServer website (resolution = 1 m/pixel).

## C. Photograph and Computer Image Techniques

Several options are available to estimate landscape areas from
orthophotographs. The methods available depend on the image format:
hardcopy or digital. Regardless of format, the first step requires
identifying boundaries between landscape and non-landscape areas. In
many cases, a site visit is necessary. This provides an opportunity to
define boundaries, which will improve the results.

Once boundaries are established on a photograph, there are several
methods to determine areas:

-   Counting squares

-   Subdividing the areas in geometric shapes

-   Planimeter

-   Computer software packages

### 1. Counting Squares

Grid paper is placed over the photograph and the number of squares in
the landscape area are counted. If the image scale and the number of
squares per unit area are known, then area can be calculated (Appendix
A). The accuracy of this method depends on the size of the squares and
the individual's ability to accurately count squares in each area. The
higher the number of squares per unit area, the greater the accuracy,
but also the more time required to count the squares.

### 2. Geometric Shapes

Geometric shapes are placed over landscaped areas on orthophotographs.
Measured lengths and widths from the orthophotographs are used to
calculate the geometric shape areas. Again, the challenge is finding
geometric shapes that adequately approximate the entire landscape area.
Appendix A contains details on this method.

### 3. Planimeter

A planimeter calculates the area of a shape as it traces the shape's
perimeter (Figure 12). This method can be used on areas of any shape.
The output of the planimeter is either in^2^ or mm^2^. The
orthophotograph's scale must be known to convert the planimeter reading
into square feet or square meters. Most agencies have planimeters in
their engineering department. This instrument requires some skill and
practice on images of known areas.

![](media/image13.png){width="3.3833333333333333in"
height="1.8611111111111112in"}

[]{#__RefHeading___Toc438353541 .anchor}Figure 12. Planimeter for area
determination from printed orthophotographs.

With planimeters, boundaries must be determined; it may be helpful to
draw the boundaries directly on the orthophotographs. In order to
account for errors in the measurement process, measure the same area
multiple (minimum of three) times (without zeroing out the instrument
each time), and then divide the final area by the number of passes. This
will give an average area. This technique usually results in accuracy
ranging from 2 - 5%. The error can come from two sources: operator error
or misinterpretation of the boundaries.

When operating a planimeter, each slight hand movement can result in
error. It can be difficult to hold your hand steady for the amount of
time required to measure some areas. Small landscape areas (1 in^2^ or
less) should be printed at a larger scale (factor of 2-4) before
measuring. This will reduce error due to slight hand movements. In most
parks, trees will block some of the boundaries causing interpretation
problems. It is essential that whoever determines boundaries has
personal knowledge of the park. Again, site visits are critical.

### 4. Computer Software

Geographic Information Systems (GIS) software provides another option
for measuring areas on orthophotographs. For this project, ArcView^®^
was used. However, there are other types of software that can be used
for this same purpose. Orthophotographs can be opened in ArcView^®^ as
*themes* or *layers* (Figure 13).

![](media/image14.png){width="3.841666666666667in"
height="2.7916666666666665in"}

[]{#__RefHeading___Toc438353542 .anchor}Figure 13. Orthophotograph of
Santa Rosa Park inserted as a theme in ArcView^®^.

Orthophotographs created by professional engineering/surveying companies
should transfer directly into ArcView^®^. Appendix C contains
information regarding transferring orthophotographs obtained off the
Internet into ArcView^®^.

The accuracy of this process depends on correctly identifying the
landscape boundaries and the resolution of the orthophotograph. Once
again, personal knowledge of the site is critical in determining correct
boundaries.

# III. Procedures

## A. Sites

Three parks were chosen to evaluate selected area measurement methods:
French Park, Mitchell Park, and Santa Rosa Park. Each park is in San
Luis Obispo, California. These parks were chosen because they represent
a wide range of size, shape, and age of landscapes.

French Park is the newest of the parks and contains 9.7 acres (7.7 acres
landscaped). The landscape boundaries are easily identified and seen
from aerial photographs. The landscape consists of many parcels covering
a wide range of sizes.

Mitchell Park is the oldest of the parks and is located close to
downtown. The park covers one city block with a senior citizen center in
the northeast corner of the block. There are many mature trees that
obscure the landscape boundaries in the aerial photographs. A majority
of the landscape consists of relatively small areas.

Santa Rosa Park is a mature park containing 8.2 acres (5.3 acres
landscaped). Most of the park is contained in three large turf areas.
There are eight additional areas with turf and flowerbeds. Trees obscure
some of the boundaries. Table 1 summaries the size and size distribution
information for each park.

[]{#__RefHeading___Toc438353517 .anchor}Table 1. Landscape areas of
French, Mitchell, and Santa Rosa Parks measured with 1 cm GPS.

+----------------------------+-------------+-------------+-------------+
|                            | French      | Mitchell    | Santa Rosa  |
+----------------------------+-------------+-------------+-------------+
| Total Area (acres)         | 9.7         | 3.4         | 8.2         |
+----------------------------+-------------+-------------+-------------+
| Total Area (ft^2^)         | 422,000     | 146,000     | 359,000     |
+----------------------------+-------------+-------------+-------------+
| Landscape Area             | 80%         | 63%         | 64%         |
+----------------------------+-------------+-------------+-------------+
| Hardscape Area             | 20%         | 37%         | 36%         |
+----------------------------+-------------+-------------+-------------+
| Number of Landscape        | 19          | 5           | 11          |
| Sub-areas                  |             |             |             |
+----------------------------+-------------+-------------+-------------+
| Smallest Landscape         | 580         | 1360        | 36          |
| Sub-area                   |             |             |             |
|                            |             |             |             |
| (ft^2^)                    |             |             |             |
+----------------------------+-------------+-------------+-------------+
| Largest Landscape Sub-area | 147, 600    | 35, 100     | 75, 700     |
| (ft^2^)                    |             |             |             |
+----------------------------+-------------+-------------+-------------+
| Sub-area Size (ft^2^)      | Number of   |             |             |
|                            | Sub-areas   |             |             |
|                            | With a      |             |             |
|                            | Given Size  |             |             |
+----------------------------+-------------+-------------+-------------+
| > \< 1000                  | 1           | 0           | 6           |
+----------------------------+-------------+-------------+-------------+
| > 1000 - 5000              | 9           | 1           | 2           |
+----------------------------+-------------+-------------+-------------+
| > 5,000 - 10,000           | 3           | 0           | 0           |
+----------------------------+-------------+-------------+-------------+
| > 10,000 - 50,000          | 4           | 4           | 0           |
+----------------------------+-------------+-------------+-------------+
| > \> 50, 000               | 2           | 0           | 3           |
+----------------------------+-------------+-------------+-------------+

## B. Reference Area Measurements

Survey grade GPS (cm accuracy) in real time kinematic (real time
measurements) was used to determine the area of the landscape for each
park. These measurements were used as a basis of comparing the other
measurement methods.

In French Park, the GPS measurements were easy because of the openness
of the park. The park is relatively new; thus the trees and shrubs are
small. The openness of the area enables the GPS receiver to obtain the
necessary satellite signals. Measurements were made around the entire
park boundary and each hardscape boundary. In this case, landscape area
was computed by subtracting the hardscape area from the total area. This
procedure was chosen because it was easier to measure the hardscape
areas directly in this park.

Survey quality GPS measurements were much more difficult in Mitchell
Park. The tall mature trees interfered with the reception of the GPS
signal. The best time of day to take measurements was estimated using
Trimble GPS Planner software (www.trimble.com). The best time of day
depended on the number of visible satellites with good spatial
distribution. In areas where direct measurements could not be taken,
offset measurements and conventional surveying techniques were employed.
An offset measurement relates a new position to a known position by the
distance and direction of a line connecting the two points. The lengths
and directions of offset lines were made using a tape and compass.

When taking measurements at Santa Rosa Park the same difficulties were
encountered in some areas as at Mitchell Park. Again, offset
measurements were used where direct measurements could not be taken.

## C. Field Measurements

### 1. Global Positioning System

![](media/image15.wmf)GPS measurements of each park were taken with a
Trimble ProXL^®^ instrument (1 m level accuracy). The California
Conservation Corps (CCC) has a program to measure key features in parks
and cities with this instrument (Appendix D). Personnel from CCC
measured each of the park's landscape areas (Figure 14). The instrument
took location measurements every three seconds as they walked an area
perimeter. They also took measurements where boundary direction changes.
At several points in Mitchell and Santa Rosa Parks, they also used
offset measurements. Trimble Pathfinder^®^ software was used to analyze
the GPS data and create a file for use in ArcView^®^.

[]{#__RefHeading___Toc438353543 .anchor}Figure 14. CCC members using a
Trimble ProXL^®^ for GPS readings.

### 2. Compass and Odometer Wheel

Landscape areas were determined by traversing each area using a compass
and odometer wheel. Traversing each area consisted of dividing the
boundary into a series of line segments. The length and bearing of each
line segment was measured. The traverse data was entered into TDS Survey
Pro^®^ software that adjusted data to account for random errors. The
software calculated areas based on the measurements. The area of
rectangular flowerbeds was determined by measuring the length and width
of the area.

### 3. Laser Rangefinder

Due to limited access to a laser rangefinder, only two medium landscape
areas were measured with this device. The rangefinder had a built-in
compass; thus both distance and bearing were measured. Distance and
bearing data was measured and recorded from a point inside the landscape
area to the area boundary. The data was entered into AutoCad^®^ software
to create a map and determine landscape areas.

## D. Image Based Measurements

### 1. Computer Software

Aerial orthophotographs at 1ft/pixel and 1m/pixel were analyzed to
determine the landscape areas of each park. The 1 m/pixel
orthophotographs were downloaded from the Microsoft site. The 1 ft/pixel
orthophotographs were taken by City of San Luis Obispo and were
available on-line: *ftp:estrella.acs.calpoly.edu*. Orthophotographs were
imported into ArcView^®^. In ArcView^®^ a tracing function outlined
landscape areas to create polygons. Site visits were done to verify
boundary locations on the orthophotographs. Once the polygons were
defined, ArcView^®^ calculated landscape areas.

### 2. Planimeter

Orthophotographs were printed from ArcView^®^ at a scale of 1\" = 100
ft\" on a laser printer. Lines were drawn by hand around each landscape
area, and a planimeter was used to measure the areas. Again, site visits
were done to verify boundary locations on the orthophographs. Three
measurements were taken and averaged for each area.

# IV. Results

Results from field and office measurements are summarized in Table 2.
Results compare each method for determining the landscape areas. The
areas computed from the GPS (1cm) data were used as a reference and
basis for comparison. All of the technologies and methodologies
investigated resulted in area measurements within 7% of the reference
values.

[]{#__RefHeading___Toc438353518 .anchor}Table 2. Comparison of area
measurements for each method.

  ---------- ----------- --------- --------- --------- ------------ --------- -------------- ---------
             Reference             Field               Image Based                           
             Area                  Based                                                     
             (ft^2^)                                                                         

  Park                             GPS (1 m) Wheel and ArcView^®^             Planimeter\*   

                                             Compass   1 ft/pixel   1 m/pixel 1 ft/pixel     1 m/pixel

  French     337,500     area      336,800   346,000   336,500      319,800   322,000        305,000
                         (ft^2^)                                                             

             320,000\*   error (%) -0.2%     2.5%      -0.3%        -0.1%     -4.6%          -4.7%

  Mitchell   91,300                90,000    92,000    97,500       97,000    95,000         97,000

                                   -1.4%     0.8%      6.8%         6.2%      4.1%           6.2%

  Santa Rosa 229,860               227,000   229,000   232,000      223,000   233,000        232,000

                                   -1.2%     -0.4%     1.0%         -3.0%     1.4%           1.0%
  ---------- ----------- --------- --------- --------- ------------ --------- -------------- ---------

\* The 1 m/pixel aerial photographs taken from the Internet were missing
a portion of French Park. The reference area was adjusted for the
methods that involved this aerial photograph.

Table 3 summarizes sub-area measurements for Santa Rosa Park. The areas
are listed by size and method of measurement. The range in percent error
is widespread, the largest occurring with the smaller areas.

[]{#__RefHeading___Toc438353519 .anchor}Table 3. Percent error for each
measurement method for Santa Rosa Park.

  ----------- --------- -------- -------------- ------- --------- ------- ------------ -------- --------- -------
  Reference   Field              Image Based                                                              
              Based                                                                                       

  GPS         Wheel and          Computer                                 Planimeter                      
              Compass            Software                                                                 
                                 (ArcView^®^)                                                             

                                 1 ft/pixel             1 m/pixel         1 ft/pixel            1 m/pixel 
                                 photo                  photo             photo                 photo     

  ft^2^       ft^2^     \% Error ft^2^          \%      ft^2^     \%      ft^2^        \% Error ft^2^     \%
                                                Error             Error                                   Error

  36          39        -8.3%    43             19.4%   \*        \*      \*           \*       \*        \*

  60          60        0.0%     65             8.3%    \*        \*      82           36.7%    \*        \*

  98          108       -10.2%   97             -1.0%   \*        \*      \*           \*       \*        \*

  192         220       -14.6%   180            -4.7%   \*        \*      \*           \*       \*        \*

  303         224       26.1%    280            -7.6%   \*        \*      230          -24.1%   \*        \*

  935         950       -1.6%    880            -5.6%   \*        \*      810          -13.4%   \*        \*

  1868        1880      -0.6%    1830           -2.0%   \*        \*      1630         -12.7%   \*        \*

  4030        3990      1.0%     3700           -8.1%   \*        \*      3600         -10.7%   \*        \*

  72800       70600     3.0%     75200          3.3%    75200     3.3%    76000        4.4%     68000     -6.6%

  73800       73000     1.1%     73600          -0.3%   69100     -6.3%   75000        1.6%     78300     6.1%

  75700       78000     -3.0%    75900          0.2%    73600     -2.7%   76000        0.4%     70600     -6.7%
  ----------- --------- -------- -------------- ------- --------- ------- ------------ -------- --------- -------

\* Because of the limited visibility in the aerial photographs not all
of the smaller individual areas could be obtained.

Due to the limited access to a laser rangefinder, only two landscape
areas were measured using this instrument. Table 4 summarizes results of
the areas measured by the laser rangefinder.

[]{#__RefHeading___Toc438353520 .anchor}Table 4. Landscape areas
determined with a laser rangefinder.

  ----------------------- ----------------------- -----------------------
  **Reference Area\       **Measured Area\        **Difference\
  (ft^2^)**               (ft^2^)**               (%)**

  60,000                  61,900                  3.2

  7,760                   7,990                   3.0
  ----------------------- ----------------------- -----------------------

The hours required in the field (collect data) and in the office
(analyze data) vary by method (Table 5). Labor costs represent estimates
of hiring someone with the appropriate skills/knowledge to complete the
tasks.

[]{#__RefHeading___Toc438353521 .anchor}Table 5. Labor costs associated
with determining landscape areas in parks.

  ---------------------------------------------------------------------------------------
  Park       Technique          Time                Total   Cost      Total   
                                Required            Time              Cost    
                                (hrs)                                         
  ---------- ------------------ ---------- -------- ------- --------- ------- -----------
                                Field      Office   (hrs)   (\$/hr)   (\$)    (\$/acre)

  French     GPS 1M Accuracy    5          2        7       20        140     14

  (337,500   Compass & Wheel    10         2        12      20        240     25
  ft^2^)                                                                      

             Orthophoto &       1.0        1        2       20        40      4
             ArcView^®^                                                       

             Orthophoto &       1.5        1        2.5     20        50      5
             Planimeter                                                       

  Mitchell   GPS 1M Accuracy    4          1        5       20        100     29

  (91,300    Compass & Wheel    10         2        12      20        240     71
  ft^2^)                                                                      

             Orthophoto &       1.0        1        2.0     20        40      12
             ArcView^®^                                                       

             Orthophoto &       1          1.5      2.5     20        50      15
             Planimeter                                                       

  Santa Rosa GPS 1M Accuracy    4          2        6       20        120     15

  (229,860   Compass & Wheel    12         2        14      20        280     34
  ft^2^)                                                                      

             Orthophoto &       1.0        1        2.0     20        40      5
             ArcView^®^                                                       

             Orthophoto &       1          1.5      2.5     20        50      6
             Planimeter                                                       
  ---------------------------------------------------------------------------------------

# V. Discussion

In order to compare several area measurement methods and equipment,
irrigated landscape areas within three parks were measured using several
methods. The reference (standard) measurements were made using a GPS
system capable of locating points within 1 cm. The following is a
discussion of the results provided in the previous section.

A number of variables influence the performance of these techniques and
the decision-making process to determine which technique is appropriate
for a given situation.

## A. Reference Measurements

Reference measurements were taken using the same techniques and effort
that a professional surveyor would use in determining the landscape
areas of the three sample parks. Errors in reference area values are
estimated to be less than one (1) percent by following standard
surveying procedures. Errors in the reference areas are random in nature
and the result of the limits of the equipment, techniques, and
surveyors.

Accurate reference measurements can also be obtained by hiring a
professional land surveyor. The professional land surveyor uses
centimeter accurate GPS, a total station instrument, or both to provide
an accurate estimate of area and create a map of the surveyed areas. The
results obtained by professional surveyors set the standard for all
other techniques. If there is a need for a high degree of accuracy and
confidence in the results, a professional land surveyor will provide it.

Table 6 indicates the cost that a professional surveyor would charge to
determine the size of landscape areas. The \"area only\" column is
comparable to the work that was done in establishing the reference areas
for this report. The \"area with map\" column is for a more detailed map
containing not only area information but also topographic and vegetation
information. The accuracy of this work would be within one (1) percent.
The costs in Table 5 and Table 6 are not directly comparable. The cost
data in Table 6 includes labor, equipment, training, overhead, and
profit. The cost data in Table 5 includes only the cost of labor at an
assumed hourly wage.

The difference in costs indicates that obtaining the guaranteed high
level of accuracy from a professional surveyor is significantly more
expensive than the cost of using less accurate methods.

[]{#__RefHeading___Toc438353522 .anchor}Table 6. Equivalent professional
surveyor costs for area measurement in this study.

  -------------- ------------ ----------- ----------- ----------- -----------
  Park           Park Area    Area Only\*             Area with   
                                                      Map\*\*     

                              Total Cost              Total Cost  

                 (Acres)      \$          \$/Acre     \$          \$/Acre

  French Park    9.7          \$1500      \$155       \$3500      \$361

  Mitchell Park  3.4          \$1000      \$294       \$3000      \$882

  Santa Rosa     8.2          \$2000      \$244       \$4500      \$549
  Park                                                            
  -------------- ------------ ----------- ----------- ----------- -----------

\* Provides a point plot showing the landscape areas as closed polygons.

\*\* Provides a topographic map showing contours, limits of landscape
type (i.e., planter vs. trees vs. turf) and edge of hardscape.

## B. Comparison of Techniques

Measurement technologies were evaluated on the following criteria:

-   Equipment required

-   Cost of equipment

-   Cost of analysis

-   Accuracy and precision

-   User knowledge/skill

The selection of a method or combination of methods will depend on
finding compromises between cost and accuracy. The higher the accuracy
required the greater the cost. The range of costs and level of required
skills are summarized in Table 7. It is important to note that the cost
of the various methods ranges from a few thousand dollars to \$30,000 or
more. Of course, the easiest way to reduce the average equipment cost is
to make full use of the equipment. The cost of these methods varies
considerably, while errors range from 1% to 8%. The costs are also
influenced by the availability of aerial orthophotos, computer
equipment, software, and personnel skill levels.

[]{#__RefHeading___Toc438353523 .anchor}Table 7. Summary of costs and
constraints for area determination methods.

+--------+------+--------+------+------+-----------+----+----+----+
| *      | **E  | **So   | **   | **Ac | **Time    | ** | ** | *  |
| *Techn | quip | ftware | Soft | cura | Spent in  | Ti | Re | *L |
| ique** | ment | Used   | ware | cy** | Field**   | me | qu | ab |
|        | Co   | for    | Co   |      |           | f  | ir | or |
|        | st** | Anal   | st** |      |           | or | ed | Co |
|        |      | ysis** |      |      |           | An | S  | st |
|        |      |        |      |      |           | al | ki | (  |
|        |      |        |      |      |           | ys | ll | \$ |
|        |      |        |      |      |           | is | \* | /A |
|        |      |        |      |      |           | ** | ** | cr |
|        |      |        |      |      |           |    |    | e) |
|        |      |        |      |      |           |    |    | ** |
+--------+------+--------+------+------+-----------+----+----+----+
| GPS    | \    | T      | C    | 1 cm | 5-6 hrs.  | 1  | 5  |    |
|        | $20, | rimble | omes | H    | depending | hr |    |    |
| cm     | 000- | Survey | w/   | oriz | on        |    |    |    |
| ac     | \$30 | Office | E    |      | satellite |    |    |    |
| curacy | ,000 |        | quip | 2 cm | positions |    |    |    |
|        |      |        | ment | Vert | and       |    |    |    |
|        |      |        |      |      | number of |    |    |    |
|        |      |        |      | \<1% | points    |    |    |    |
|        |      |        |      |      | taken, 30 |    |    |    |
|        |      |        |      | Used | seconds   |    |    |    |
|        |      |        |      | to   | to 1      |    |    |    |
|        |      |        |      | d    | minute    |    |    |    |
|        |      |        |      | eter | per point |    |    |    |
|        |      |        |      | mine | taken     |    |    |    |
|        |      |        |      | r    |           |    |    |    |
|        |      |        |      | efer |           |    |    |    |
|        |      |        |      | ence |           |    |    |    |
|        |      |        |      | area |           |    |    |    |
+--------+------+--------+------+------+-----------+----+----+----+
| GPS    | \$   | T      | C    | 1    | 2-3 hrs.  | 1  | 5  | \  |
|        | 5000 | rimble | omes | %-2% | depending | hr |    | $1 |
| 1 m    |      | Path   | w/   |      | on        |    |    | 5- |
| ac     |      | finder | E    |      | satellite |    |    | \$ |
| curacy |      | So     | quip |      | positions |    |    | 30 |
|        |      | ftware | ment |      | and       |    |    |    |
|        |      |        |      |      | number of |    |    |    |
|        |      |        |      |      | points    |    |    |    |
|        |      |        |      |      | taken,    |    |    |    |
|        |      |        |      |      | 3-5       |    |    |    |
|        |      |        |      |      | seconds   |    |    |    |
|        |      |        |      |      | per point |    |    |    |
|        |      |        |      |      | taken     |    |    |    |
+--------+------+--------+------+------+-----------+----+----+----+
| Wheel  | Wh   | 1a.    | 1a.  | 1    | 5-6 hrs.  | 1  | 3  | \  |
| and    | eel: | TDS-48 | \    | %-3% | depending | hr |    | $1 |
| C      | \$50 | Survey | $995 |      | on size   |    |    | 5- |
| ompass | -200 | Pro^®^ |      |      | and       |    |    | \$ |
| \*\*   |      | to use | 1b.  |      | number of |    |    | 70 |
|        | Comp | with   | \    |      | areas,    |    |    |    |
|        | ass: | HP 48  | $995 |      | and       |    |    |    |
|        |      | GX^®^  |      |      | number of |    |    |    |
|        | \$10 | Calc   | 2\.  |      | mea       |    |    |    |
|        | 0-\$ | ulator | \$   |      | surements |    |    |    |
|        | 1500 |        | 3750 |      | taken     |    |    |    |
|        |      | 1b.    |      |      |           |    |    |    |
|        |      | TDS    | 3\.  |      |           |    |    |    |
|        |      | -Forsi | \$   |      |           |    |    |    |
|        |      | ght^®^ | 1755 |      |           |    |    |    |
|        |      |        |      |      |           |    |    |    |
|        |      | 2\.    |      |      |           |    |    |    |
|        |      | Auto   |      |      |           |    |    |    |
|        |      | Cad^®^ |      |      |           |    |    |    |
|        |      |        |      |      |           |    |    |    |
|        |      | 3\.    |      |      |           |    |    |    |
|        |      | T      |      |      |           |    |    |    |
|        |      | erraMo |      |      |           |    |    |    |
|        |      | del^®^ |      |      |           |    |    |    |
|        |      |        |      |      |           |    |    |    |
|        |      | \*\*   |      |      |           |    |    |    |
+--------+------+--------+------+------+-----------+----+----+----+
| Plan   | \$   | None   |      | 2    | 1 hr      | 1  | 2  | \$ |
| imeter | 200- |        |      | %-8% |           | hr |    | 5- |
|        | \    |        |      |      |           |    |    | \$ |
|        | $600 |        |      |      |           |    |    | 15 |
+--------+------+--------+------+------+-----------+----+----+----+
| ArcV   |      | ArcV   | \$   | 0.1  | 1 hr      | 1  | 2  | \$ |
| iew^®^ |      | iew^®^ | 1200 | %-7% |           | hr |    | 5- |
|        |      |        |      |      |           |    |    | \$ |
|        |      |        |      |      |           |    |    | 10 |
+--------+------+--------+------+------+-----------+----+----+----+
| Laser  | \$50 | TDS-48 | \    | 0    | Same as   | Sa | 3  |    |
| Range  | 0-\$ | Survey | $995 | .5-3 | wheel and | me |    |    |
| finder | 5000 | Pr     |      | ft   | compass   | as |    |    |
|        |      | o^®^to |      |      |           | w  |    |    |
|        |      | use    |      |      |           | he |    |    |
|        |      | with   |      |      |           | el |    |    |
|        |      | HP 48  |      |      |           | a  |    |    |
|        |      | GX^®^  |      |      |           | nd |    |    |
|        |      | Calc   |      |      |           | c  |    |    |
|        |      | ulator |      |      |           | om |    |    |
|        |      |        |      |      |           | pa |    |    |
|        |      |        |      |      |           | ss |    |    |
+--------+------+--------+------+------+-----------+----+----+----+

\* Rating of 1-5 for Required Knowledge or Skill of User

1.  No training required, simple to use

2.  Minimal training, should have some knowledge of computers to use
    ArcView^®^

3.  Some surveying skills required, training sessions required

4.  Surveying background required, training sessions recommended

5.  Surveying background required, training required, knowledge of
    computers

\*\*Any of the three software packages can be used to analyze the data.

### 1. Field Based

Field based techniques are more consistent than image based techniques
and provide results with errors less than 2.5% (Table 2). Because they
are field based, identifying the boundaries becomes much easier. In this
study, using the 1 meter accurate GPS equipment is similar to using the
1 centimeter accurate GPS equipment used in establishing the reference
areas.

Field surveying with 1 meter accurate GPS equipment provides consistent
and accurate measurements. This method had the smallest range of errors
(0.2% to 1.4%). Large areas are measured quickly by walking the area
boundary. Tall and mature trees in Mitchell and Santa Rosa Parks caused
difficulties in locating certain points. It is important to know
conventional surveying techniques to handle these types of difficulties.

In addition to area measurements, maps can be created from the GPS data
and imported into GIS software. Use of the equipment requires some
training, but the field operation is straightforward. Someone
knowledgeable in GPS should be part of the measurement team. Given the
cost of equipment and required training, unless there is going to be
extensive use of the equipment, a consultant would be more
cost-effective for some agencies. Members of the GPS group in the
California Conservation Corps are knowledgeable and very capable of
completing this kind of work (Appendix D).

Traversing landscape areas with a compass and odometer wheel is a
\"simple form\" of a professional surveyor using a total station. Again
the errors are relatively consistent, ranging from 0.4% to 2.5%. The
greatest errors in this method arise from environmental conditions that
affect the performance of the compass. For example, taking compass
readings near metal objects (e.g. cars, steel fences, and steel light
posts) will cause the compass to read incorrectly. Most districts should
have personnel that are able to use the compass and odometer wheel
technique with some training. This type of equipment is generally
available in most organizations.

The laser rangefinder is a \"high tech\" version of the compass and
odometer wheel. Its accuracy should be greater than the compass and
odometer wheel based on the equipment specifications. Several laser
rangefinders interface with electronic field books that help automate
data collection and analysis. Whether the laser rangefinder is worth the
additional cost (approximately \$5,000) depends on the district\'s
ability to fully utilize the equipment. The error associated with using
the laser rangefinder on several landscape areas was about 3%. To ensure
that measurements are to the correct point, a target should be used with
a laser rangefinder. The digital output of the laser rangefinders makes
it easy to read the instrument\'s output data. Rangefinder readings are
faster than measurements using a compass and odometer wheel.

### 2. Image Based

Image based techniques require the least amount of surveying knowledge.
Personnel with reasonable computer skills can learn GIS software and
take the measurements. It is likely that orthophotographs already exist
for many parks. This method has the greatest variability due to the
orthophotographs\' resolution, image size, and location and amount of
vegetation in the park.

Orthophotographs (1 m/pixel resolution) obtained from the Microsoft
TerraServer website were easy to obtain and use. The site is evolving
and will eventually cover all of California. The higher resolution
orthophotographs (1 ft/pixel resolution) obtained from the City of San
Luis Obispo showed excellent detail in each park. It is very likely that
municipal, county, and engineering/planning departments currently have
orthophotographs of their areas. Aerial photography companies can be
another source for orthophotographs. Photographs can be purchased from
these companies as printed or digital images. Locating these
orthophotographs may take some searching, but it is worth the effort.

Errors of aerial photograph based techniques may be significant due to
difficulties in determining boundaries in parks with mature trees. In
French Park, where boundaries are easily seen, the error is less than
0.3%. In Mitchell Park, with its large number of mature trees, the error
approaches 7%. As expected, 1 ft/pixel photographs more clearly
delineate the boundaries, thus reducing the errors as compared to those
based from 1 m/pixel photographs. Some of these problems can be
mitigated using a map hard copy at the site to verify boundaries.

Measuring photograph areas using a planimeter is less accurate than
using ArcView^®^ software. This is due to the inherent inaccuracy in
using a planimeter. Up to 4% error can be directly attributed to the
planimeter. The rest of the error is a result of incorrectly identifying
the landscape boundary. Orthophotographs for use with a planimeter can
be downloaded from the Internet. Printed documents of these downloadable
orthophotographs are not available. Local aerial photographers may have
pictures available at an appropriate scale.

## C. General Measurement Issues

### 1. Size of Landscape Areas

While the errors for an entire park may be acceptable, errors within
individual parcels in the park may be very large (Table 4). In general,
as landscape areas increase the errors in measurement decrease. Also,
measured areas of irregular shapes have more error than regular shapes.

For example, a 100 ft line measured with a 3 ft accuracy could have an
error up 3%. A 1,000 ft line measured to the same accuracy would have an
error up to 0.3%. In addition, selecting the appropriate number and
length of straight-line segments to represent a curved line is
influenced by the parcel size. The larger the parcel the smaller the
impact the straight-line estimation has on the area.

It is also important to note that the three largest areas represent
almost 97% of the entire landscape area of Santa Rosa Park. Re-computing
the error based on the three largest areas is shown in Table 8. The
errors are less than 5.6% when including only the three largest areas.
This example demonstrates the importance of measuring the area of large
pieces of the landscape with very accurate methods and using less time
consuming methods on smaller parcels of the landscape. The focus should
be to ensure that the larger areas are measured as accurately as
possible. Smaller sub-areas measured with less accurate methods will
have little affect on the final results.

Table 8. Santa Rosa Park errors considering only the largest landscape
areas.

<table>
<colgroup>
<col style="width: 8%" />
<col style="width: 8%" />
<col style="width: 8%" />
<col style="width: 7%" />
<col style="width: 8%" />
<col style="width: 7%" />
<col style="width: 8%" />
<col style="width: 7%" />
<col style="width: 8%" />
<col style="width: 7%" />
<col style="width: 8%" />
<col style="width: 7%" />
</colgroup>
<tbody>
<tr class="odd">
<td></td>
<td><p>Reference Area (GPS)</p>
<p>(ft<sup>2</sup>)</p></td>
<td>Wheel and Compass<br />
(ft<sup>2</sup>)</td>
<td>Error<br />
<br />
<br />
(%)</td>
<td><p>ArcView<sup>®</sup></p>
<p>1 ft/pix photo<br />
(ft<sup>2</sup>)</p></td>
<td>Error<br />
<br />
<br />
(%)</td>
<td><p>ArcView<sup>®</sup></p>
<p>1m/pix photo<br />
(ft<sup>2</sup>)</p></td>
<td>Error<br />
<br />
<br />
(%)</td>
<td><p>Planimeter</p>
<p>1 ft/pix photo<br />
(ft<sup>2</sup>)</p></td>
<td>Error<br />
<br />
<br />
(%)</td>
<td><p>Planimeter</p>
<p>1 m/pix photo<br />
(ft<sup>2</sup>)</p></td>
<td>Error<br />
<br />
<br />
(%)</td>
</tr>
<tr class="even">
<td>Three Largest areas</td>
<td>229,860</td>
<td>221,600</td>
<td>-3.6</td>
<td>224,600</td>
<td>-2.3</td>
<td>218,000</td>
<td>-5.2</td>
<td>227,000</td>
<td>-1.2</td>
<td>216,900</td>
<td>-5.6</td>
</tr>
<tr class="odd">
<td>All areas</td>
<td>229,860</td>
<td>229,000</td>
<td>0.37</td>
<td>232,000</td>
<td>0.93</td>
<td>223,000</td>
<td>-3.0</td>
<td>233,000</td>
<td>1.37</td>
<td>232,000</td>
<td>1.0</td>
</tr>
</tbody>
</table>

### 2. Confidence in Data

With any of these techniques, it is important to have a method to check
the results. Mistakes are caused not by the inaccuracy of the equipment
or process, but by misapplication of the technique, incorrect data
collection, transposition of recorded numbers, etc. Without a way to
reaffirm the results, it is difficult to place confidence in the
results. A simple way to check the work is to compare the sum of all the
areas in the park to the total park area. The total area may be
estimated by traversing the entire park boundary. This approximation
will detect mistakes in the measurements.

Another approach to checking completed work is to compare it to an
approximation from some other source. A plot map or construction map may
have approximate areas listed. Areas can be estimated by using simple
geometric shapes. If the method being used includes field-based work,
check the results with those from an image based technique and vise
versa. In this project all fieldwork was superimposed over
orthophotographs of each area to catch mistakes. Several were identified
but easily corrected.

### 3. Costs and Resource Availability

Estimating costs associated with collecting and analyzing data is
difficult because of the variables involved with each method. Equipment
and training costs vary widely depending upon resource availability and
number of parks. Estimates for the labor in making these measurements
are shown in Table 6. The labor cost per acre of a given technique can
vary by more than 100% depending upon specific park conditions. Many
small areas and extensive non-turf vegetation increase costs of
collecting and analyzing data. The labor cost of image-based techniques
is significantly less than field-based techniques since it takes more
time to walk around a park than it does to review images.

Much of the equipment and software discussed in this report may exist in
many of the water districts. Project leaders must check across district
divisions to locate equipment, software, and expertise. From the
discussion with selected water districts, it appears that human
resources will only be available when landscape area measurement becomes
a high priority in their organization. Hiring an outside consultant,
such as the California Conservation Corps and others, to take the
measurements may be a viable option. By using an outside group, there is
no need to disrupt existing projects or obtain new equipment, software
or human resources. If the measurements are to be completed within the
agency, personnel training may be needed. General training can be
obtained from colleges and universities. Specific training may be
available by consultants.

# VI. Conclusions

Based on the evaluation of data collected for this project, a simple
criteria may be used to select the best approach for measuring landscape
areas. Before selecting a method(s), several pieces of information are
needed: acceptable accuracy; availability and cost of existing
resources; cost of acquiring additional resources; and nature of sites
to be measured (i.e., old vs. new plantings, large turf areas, irregular
shapes, site size, number of sites, etc.). This will allow for an
adjustment based on specific constraints. The procedure outlined below
has also been summarized in Appendix G.

## Choosing a Method

**Determine the required accuracy**. If the organization requires less
than 1% error, use a professional surveyor. They are trained and
licensed to complete area measurement with a high degree of accuracy.
They can produce maps containing additional field information that may
be shared with other projects, thus reducing the cost of collecting area
information. If the acceptable error is greater than 1%, other options
will be acceptable.

**Determine image availability and nature of site**. If good quality
orthophotographs are available, use them with GIS software (e.g.,
ArcView^®^). Small areas, or areas where the boundaries are not visible,
will require trying to identify boundaries in the field. Orthophoto/GIS
approach is well suited to larger landscape areas. Errors less 3% can be
expected under these conditions. If acceptable orthophotographs do not
exist, use GPS (1 meter accuracy). This method is appropriate for
virtually all sized areas (except for extremely small areas). Large
areas can be traversed quickly, and the error will be less than 2%.

**Determine availability of field-based equipment**. If GPS is
available, use this method for field measurements. If GPS is not
available or acceptable, then use a compass and odometer wheel to
traverse each area. This works well for small and medium size areas.
Errors may be less than 3%. Very small areas can be evaluated using
simple geometric shapes.

**Determine if planimeter use is acceptable**. Using a planimeter to
measure areas on orthophotographs is the least accurate method. Errors
up to 7% can be expected. If this amount of error is acceptable, then
this method can be used if acceptable orthophotographs exist.

## Approach and Process

The following conclusions apply to the measurement *approach and process
used*.

**Largest Areas.** Spend the most effort in accurately measuring the
largest of the sub-areas in a park. The large parcels have the greatest
influence on the entire landscape area.

**Checking Procedures.** Develop procedures to check the work for
mistakes. Without a check of the work, little confidence can be placed
in the results.

**Combine Approaches**. A combination of approaches is likely to provide
the best approach to the overall project. Use the best technique for the
given conditions.

**Record Keeping**. Entities with a large number of parks need to
consider the large volume of data that will be collected. Keeping track
of the data will be challenging. Consider hiring a consultant to address
this issue.

**Image Consideration.** Image based methods have the advantage of least
cost and reasonable accuracy, provided the quality orthophotographs have
resolutions of 1 m/pixel or better.

**Field Consideration.** Field based methods are the most consistent in
accuracy and are appropriate for all types of terrain and vegetation.
These methods will work when image based methods provide unacceptable
results.

# VII. Recommendations

The following are recommendations to facilitate the objectives of the
\"Best Management Practices,\" specifically those dealing with water
budgeting and landscape area measurement. These tasks could be supported
by the United States Bureau of Reclamation and/or additional cooperating
agencies.

**Develop Criteria**. Provide a forum for the development of measurement
criteria that would include, but not be limited to the following issues:

1.  Accuracy of measurement

2.  Definition of landscape area and boundaries

3.  Assimilation of information into databases

4.  Cost estimates for area measurement (equipment and labor)

**Training**. Provide support for measurement techniques training. This
training could range from large classes conducted at a central location
to individual instruction at the cooperator location. It may incorporate
a combination of both strategies. This would include hands-on training
regarding various field- and image-based measurement techniques:

1.  Compass and wheel

2.  GPS (1 meter accuracy)

3.  Software application and computer setup

4.  Orthophotograph acquisition and analysis

**Equipment Pool**. Establish equipment pool for use by program
cooperators. The equipment would be stored at a central location and
shipped to cooperators on an \"as needed\" basis. This equipment would
include:

1.  GPS (1 meter accuracy)

2.  Wheel and compass

3.  Laser rangefinder

4.  Computers and software

**Technical Support.** Provide on-going technical support to cooperating
agencies. This might include questions asked and answered by phone. In
special cases, a field trip to the cooperator site may be necessary.
This support might include:

1.  On-going procedural questions

2.  Technical support for equipment set-up and trouble shooting

3.  Orthophotograph acquisition and analysis

# VIII. Glossary

**Digital Orthophoto Quadrangle** An orthophotograph that is in digital
form (for computer use) that covers a standard USGS quadrangle (7 1/2
seconds latitude and longitude to 1° latitude and 2° longitude).

**Electronic Distance Measurement (EDM)** A directed signal of several
frequencies is sent to a reflecting target and then received by the
instrument. The signal is analyzed to determine the distance to the
target.

**Global Positioning System (GPS)** A system of satellites that send
signals to the earth that can be used to determine your location
anywhere in the world.

**Graphical Information System (GIS)** A graphical approach to
presenting spatial information.

**Interior Angle** The angle between two lines that form part of the
boundary of a closed traverse.

**Laser Rangefinder** A hand held version of an electronic distance
measuring device (EDM).

**Odometer Wheel** A wheel of known diameter/circumference is rolled on
the ground to measure the distance between two points. The distance
between the two points is calculated by multiplying the number of
revolutions of the wheel by the wheel circumference.

**Orthophotograph** A photograph that has been corrected to give a
constant and known scale across the entire photograph.

**Planimeter** An instrument used to determine the area of a shape drawn
on paper. The shape is traced with a pointer and the instrument
calculates the area.

**Polar Coordinates** A method to represent the location of a point from
a reference point. The location is represented by: 1.) the distance
between the reference point and the new point and 2.) the angle between
a reference direction (usually true or magnetic north) and the line
between the new point and the reference point.

**Rectangular Coordinates** A method to represent the location of a
point from a reference point. The location is represented by a
horizontal and vertical (orthogonal) distances from the reference point
to the new point.

**Real Time Kinematic GPS (RTK GPS)** GPS instrumentation that is able
to give a location in real time.

**Significant Figures** The number of digits in a number that are valid
and thus should be retained.

**Stadia** The use of a known angle built into a surveying instrument
scope to determine the distance to an object. The distance is
proportional to the distance between the stadia lines viewed in the
surveying instrument.

**Survey Grade GPS** Global positioning system instrumentation that is
capable of centimeter accuracy.

**Total Station** A surveying instrument that combines the ability to
measure the horizontal and vertical angles between two points as well as
measure the distance to the two points.

**Traverse** A surveying process where the boundary of an area is traced
in the field and the angles and distances between points that make up
the boundary are measured. A Closed Traverse begins and ends at the same
point.

# IX. References

Brinker, R. C. and R. Minnick. 1987. The Surveying Handbook. 7^th^
Edition. Van Nostrand Reinhold, New York,

Moffitt, F.H. and H. Bouchard. 1992. Surveying. 9^th^ Edition. .
HarperCollins. New York.

USGS. 1998.
http://edcwww.cr.usgs.gov/Webglis/glisbin/guide.pl/glis/hyper/guide/usgs_doq.

Wolf, P.R. and R.C. Brinker. 1994. Elementary Surveying. 9^th^ Edition.
HarperCollins. New York.