APPLICATIONS 
The five most prominent uses for ortho- 
rectified SPOT satellite imagery on a regional 
level are: 
- Geopositioning 
- Reference Imagery 
- Aerial Inventory 
- Image Map Base 
- Aerial Assessment 
Geopositioning 
One of the most essential parts of developing 
a sound GIS is the development of a 
georeferenced base. The control that goes 
into the base has a direct effect on all the 
other data layers that are developed for that 
area, both from the point of relative 
accuracies (feature to feature) and the 
ability for the analytical capabilities of GIS 
software to work properly. They will work 
regardless of the control, but results may be 
questionable or misconstrued if the control 
factor is not taken into account. The 
software used to orthorectify the image can 
maintain the control values used, as an 
attribute of the locational pointer on the 
data image. This allows the users to directly 
compute and display geopositional values for 
any location on the image. 
Image Map Base 
The very aspects that make the SPOT image a 
good geopositional source also make a very 
valuable image source for digitization of 
graphic vector information. Anything that can 
be viewed on the image can be digitized 
through "heads up" digitizing techniques. 
Because the information is taken directly from 
the image, and the image is geopositionally 
accurate, the new vector can be compiled using 
the exact same georeferenced data. Because of 
existing raster /vector integration 
capabilities on most GIS software packages, 
SPOT imagery may be used for vector data 
development and more importantly vector data 
maintenance, for regional GIS users. 
Reference Imagery 
For regional or local users that have 
developed or are developing a large scale data 
set, the SPOT image can serve as a reference 
layer. Most mapping departments or offices 
that make use of large scale maps on a regular 
basis, have an overview reference map that 
allows them to determine which specific large 
scale map or map file they want to use to 
study or solve a specific problem. In current 
GIS systems if the data base has been 
constructed from large scale source it usually 
requires a significant amount of computer 
storage. It may take a great amount of time 
to search or "view" the entire database to 
determine which specific area is needed. 
Using an overlay grid and the SPOT mosaic 
image as a reference, the user can access 
Specific large scale areas of interest. 
Aerial Assessment 
Aerial assessment encompasses the specific 
activities that decision makers are dependent 
on during the planning, implementation, and 
maintenance of a major capital project. A 
utility company wanting to determine the best 
corridors for new transmission lines, or a 
coal company wanting to assess the impact area 
for a defined coal source, can make use of 
current imagery. Mosaicked SPOT satellite 
imagery provides an easily attainable data 
Source for assessing physical and economic 
changes that have taken place after major 
687 
engineering projects. Satellite imagery can 
be very beneficial in the data maintenance and 
on going assessment of areas of concern. SPOT 
mosaics. can also be used as a means of 
defining the exact localized areas for large 
scale analysis. 
Aerial Inventory 
Aerial inventory involves the categorizing and 
quantifying of the natural resources such as 
forest areas, mineral and energy sources, 
wetlands, agricultural lands. Natural 
resource areas may change yearly, and 
therefore the data and its functionality is 
quite dependant on timely and easy updates. 
Because orthorectified SPOT image mosaics can 
be developed within a one to two month time 
span, they provide the capabilities to quickly 
re-inventory areas for changes due to human 
interventions, natural disasters, or climatic 
changes. Also of significance is the 
"Comprehensive view" that you get with the 
SPOT data. Instead of only selected features 
being shown, you see all natural features (on 
the ground) as they appear in real life. 
CONCLUSION 
Regional users can benefit greatly from the 
information contained in the satellite imagery 
currently available. The images are 
relatively easy to attain, and with current 
software capabilities SPOT image mosaics can 
achieve positional accuracies that approach 
those associated with USGS 1:24,000 7.5 minute 
quads (used extensively by local users) and 
are much more current and easier to maintain 
than the equivalent digital data created from 
the USGS products. The SPOT image mosaic 
data sets have metric and temporal accuracies 
that significantly exceed those of an existing 
1:100,000 DLG vector "off the shelf" data set. 
In all likelihood the SPOT imagery will be 
used as a primary update source to the newly 
developed 1:24,000 DLG data when it becomes 
available. For feature completeness the 
significant benefit of the SPOT mosaic imagery 
is the real "view" of the area that they 
provide. 
The initial costs of image data bases may be 
significantly greater than for public domain 
DLG. These costs must be amortized by GIS 
operational savings which may sometimes be 
difficult to quantify. The currency, 
completeness, and positional accuracies 
coupled with the potential for automated 
extraction of GIS significant features from 
the image mosaic, as well as the ability to 
use existing DLG and SPOT imagery 
simultaneously, are all factors which can 
justify the initial expenditures. Careful 
analysis of all these factors will determine 
the cost effectiveness of SPOT image mosaic 
for individual local and regional users. 
Providing the GIS users with seamless views of 
orthorectified imagery, and with newly 
developing vector integration techniques, 
users can address many of the current problems 
associated to vector data updates. In the 
near future many users will purchase specific 
available data bases to address the needs of 
the organization, and when there is a need for 
highly accurate data, or very unique data, it 
will be developed in coordination with that 
common database, in a slower, more methodical 
and more project driven manner. Future 
launches of commercial satellite imaging 
systems will insure the continued use of this 
image data for the production and maintenance 
of map graphic data bases for regional GIS 
applications.