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THE SIGNIFICANCE OF SPOT IMAGERY TO GIS APPLICATIONS: A 
COMPARISON OF DATABASES, 
Thomas W. Lenzen, 
THEIR ACCURACIES AND USES 
Staff Scientist 
TRIFID Corporation 
St. Louis, MO 
ISPRS Commission IV 
USA 
Abstract: SPOT imagery has been available for many years, but its 
success and usefulness has been 
limited by workstation data 
handling capabilities, cost, and the lack of proven application 
need on the part of local and regional users. 
With recent 
innovations in data handling capabilities and production software, 
SPOT imagery is becoming a more useful product for a more diverse 
set of users. This paper provides a comparison of current map 
derived vector databases with SPOT raster data, considering 
accuracies and potential applications. 
The comparison will involve United States Geological Survey (USGS) 
1:100,000 Digital Line Graph (DLG) data, vector DLG data bases that 
will be developed from 1:24,000 USGS maps, and SPOT imagery. The 
data sets are compared based on the usefulness to regional level 
users, whose areas of responsibility encompass 2,500 to 250,000 
square miles. The data set accuracies discussed in the evaluation 
include metric, temporal, and feature completeness. The emphasis 
is on providing a useful understanding of the significance of SPOT 
imagery to regional GIS applications. 
Key Words: Database, Accuracy, Metric, Temporal, Feature, Regional, 
Orthorectified, Image Mosaic 
INTRODUCTION 
Many local and regional users have begun or 
are about to begin developing a map graphic 
data base, the graphic portion of a Geographic 
Information System (GIS) database. They 
address this issue in three ways, create the 
map graphic data set themselves, have someone 
create the map graphic data set with user 
specific graphic data included, or by 
purchasing map graphic data off the shelf from 
a company that creates a generic data set to 
address many potential uses. To minimize 
costs the user wants to purchase a map graphic 
data set off the shelf, that allows for the 
integration of additional user specific 
information that is needed. 
This paper will discuss and compare three "off 
the shelf" map graphic data sets for regional 
use. For the regional users there have been 
off the shelf digital databases available from 
both the USGS and private companies that 
provide vector data sets that can play a role 
in implementing a GIS. The two most common 
vector data sets are the 1:100,000 DLG and the 
U.S. Census TIGER line files. In addition the 
USGS is beginning to develop the 1:24,000 DLG 
vector data set. For this paper we have 
looked at the existing 1:100,000 DLG and the 
1:24,000 DLG that will be developed, and 
compared them to SPOT imagery, which is in 
raster form. For the comparison we are using 
SPOT imagery that has been enhanced through 
triangulation, orthorectification, and 
mosaicking to increase the positional 
accuracies of the image data. The TIGER 
vector data will not be discussed in this 
paper because the metric accuracies are no 
better than the 1:100,000 DLG vector data. 
In the past few years raster imagery has begun 
to emerge as a useable data set within the GIS 
technology, mainly due to the innovations in 
hardware and software. Users can routinely 
handle and process the large amounts of data 
associated with digital imagery. With new 
software capabilities it is possible to create 
mosaicked SPOT images, with proven metric 
accuracies of 50 feet. If you compare that to 
683 
the metric accuracies of the existing 
1:100,000 DLG and the developing 1:24,000 DLG 
you begin to see the potential for using SPOT 
imagery to support GIS applications. 
Regional Emphasis 
For discussion we will divide the users into 
three general categories; national, regional 
and local level users. The regional 
applications are the focus of the discussion. 
The regional group would include users with 
areas of concern between 2,500 and 250,000 
square miles. This level of users includes 
State and Provincial agencies concerned with 
the spatial mapping and assessment of 
activities relating to the administrative 
region. It also includes groups within states 
with more specific interests such as a state 
forestry department, department of natural 
resources, a utility company, a large county, 
or special interest groups including county 
consortiums, water shed regions, and unique 
regional environmental areas, such as the 
Great Lakes region or western desert regions. 
The users at the national level would include 
those with areas of interest larger than 
250,000 square miles, for example multiple 
state interest groups, large national interest 
groups including the U.S. Federal offices of 
Forestry or Agriculture. The local group 
would include those interested in smaller 
areas and much more geographic detail than 
what can be seen in any of these map graphic 
data sets. The groups associated with this 
level user would include counties, a 
city/county/utility consortium, or engineering 
groups. 
DATA ACCURACY 
There are three map graphic data accuracies of 
importance that are discussed here (see Table 
1). Metric or positional accuracy , temporal 
or "change over time" accuracy and feature 
completeness accuracy. All three accuracies 
effect the ability of the user to visually 
interpret the graphic information allowing for 
a comprehensive area assessment in conjunction 
with the other data sets of the GIS.