A Geographic Information System (GIS) is An organized collection of computer hardware, software, geographic data,
procedures and personnel designed to efficiently capture, store, update, manipulate,
analyze, and display all forms of geographically referenced information.
Although, the focus of a GIS is on the computer component and is most
often used just for queries and map production the most important component of of a GIS is
the data and the users and the procedures that act upon it.
A GIS is not just maps and pictures - it is a database of geographic
features and attributes describing those features. An effective GIS is completely
data-driven.
Want to know more ... ?
What is GIS? (Software Vendor Definition)
What is GIS? (Academic Definition)
More GIS-related Links than you can handle ...
ESRI Jumpstation
GIS Links and AGI Dictionary (University of Edinburgh, UK)
GIS Links (University of Utrecht, Netherlands)
GIS Research (University of Maine, USA)
GIS Metadata (Bureau of Land Management, USA)