Written by George Lienkaemper Geographic Information Systems are computer applications that enter, store, retrieve, and analyze spatial information. Data are structured into broad categories called themes, which are composed of several data layers , represented on maps as features - points, lines, and polygons.
Raster maps represent data as grid cells.
Raster data can be continuous, discrete, or classified. Individual cells are registered in space, and have specified size or resolution. Images may contain data from numerous spectral bands. A GIS has tools with which you can pan and zoom, add and delete lines, points and annotation. Some systems have more of this capability than others, but all systems have a digitizing module for data capture.