WAMS (later AMS) was an interactive, menu-driven, digitizing, and map-editing system that allowed various types of data to be captured in digital format from maps or aerial photography. Aerial photography may be used if the vertical and horizontal positions of features are required; however, horizontal positions usually provide sufficient accuracy for most geographic analyses (Niedzwiadek and Greve 1979). That said, when used with a stereo plotter, the subsystem allows full photogrammetric block adjustments of aerial photographs to obtain photoposition and orientation. This information is stored in a photographic database. When retrieved, this information can be used to set up a stereomodel on the APPS-IV. Once the stereomodel is set, accurate three-dimensional ground can be obtained to form point, line, or polygon data for input into the GIS.
Data entry operators using digitizers, therefore, digitize the horizontal locations from map sheets, and the WAMS software checks to insure that national map accuracy standards are met. Digitizing from map sheets with WAMS requires a minimum of six known geographic coordinates to accommodate georeferencing algorithms to allow for the accurate georeferencing (USFWS 1980). Digitizing, editing, and verifying digital map products are conducted in an arc/node format and are data-based only after verification and polygon formation procedures have been passed without error. WAMS is scale and projection independent, capturing map coordinates in a latitude-longitude format. The edges of adjacent maps are also checked and verified during the digitizing process so that adjacent maps can be properly aligned. (Ader and Steiner, 1981)