All such GIS should, if at all possible, include: (1) a base map, often referred to as a topographic map; (2) an airphoto mosaic; (3) thematic maps, i.e. polygon, segment, or point maps from air photo interpretation. (4) a multispectral satellite image and its products such as false-colour composites; All of these must be geo-referenced and geometrically-corrected in a common coordinate system.