What is GIS ?

Geographic Information Systems, GIS, are tools used to gather, transform, manipulate, analyze, and produce information related to the surface of the Earth. This data may exist as maps, 3D virtual models, tables, and/or lists.

GISs can be as complex as whole systems that use dedicated databases and workstations hooked up to a network, or as simple as "off-the-shelf" desktop software.

GISs play an important role in many organizations. For instance, police and fire departments may use GISs to locate landmarks and hazards, plot destinations, and design emergency routes. GISs may also be used by governments, research institutes or any other body that can't possibly handle the task of manually processing large amounts of geographical data.

Reference : Wikipedia Webopedia