Engineering needs the highest levels, perhaps quarter-meter resolution or even better. An environmental protection unit using GPS to locate rare and endangered species habitats require point accuracy to enable biologists to return to a specific breeding location. If regional planning groups are studying intelligent vehicle highway systems, they will need resolutions of three feet or better. Less accuracy may show the vehicle as being completely off the road. On the other hand, planning applications involving spatial relationships between features require much broader measurements.
Some applications require both fine and coarse resolution.
Analysts will identify a problem area in vegetation, then step up to one-meter resolution. The accuracy required for a particular GIS application usually dictates the original graphic, or basemap, from which the digitized version is made. A high-resolution scanner translates the photographic image into electrical impulses, removes the distortions inherent in aerial photography, and produces a digital elevation model. The model is then translated into a language recognized by the GIS and loaded into the computer. NAPP's plan is to photograph each state once every five years.