Each element of a map layer is given a unique ID number. These unique ID numbers tie into a database management system. This allows for the addition of attributes describing the cartographic data.
For example, Wilson has a tax parcel layer that contains cartographic information depicting the boundaries of each parcel in the county and for each parcel there are approximately 75 attributes describing the parcel. This allows a user to be able to sit at a GIS terminal, visually select an area of interest, bring any layers of interest onto the screen, and select and list information about any of these layers.
As helpful as the mapping and data query functions of a GIS are, these are not what sets it apart from other computer systems. A GIS has the ability to perform sophisticated analyses not possible on any other type of system.
Many GIS projects require information from more than one GIS layer. A project may require that information from four or five layers be combined to give an answer to a particular issue. Multiple layers can be combined to yield a new layer with the desired information.
For example, one might be looking for an optimal site to locate a new electric substation. Pertinent layers are combined and the most suitable combination of these layers can be found. The GIS system then displays one map showing all of the needed information in one easy to reference place.