In GIS, each variable is represented by a layer; this concept is illustrated in the figure.  Each data layer represents a different characteristic of the real world geographic area it is describing; here, the data layers are land use, elevation, parcels, streets, and customers.
	Objects in a layer can be represented in one of three ways: by a point, a line, or an area.  In this example, the customers are defined by points, the streets are illustrated by lines, and the parcels are described by areas.
	Layers can be overlain to produce a wide variety of maps and images, and numerous analytical functions can be used to answer questions about spatial relationships.