What is GIS?

Geographic Information Systems (GIS) is a computer system for capturing, storing, validating, integrating, manipulating, analysing and displaying data related to positions on the Earth's surface. 

Typically, GIS is used for handling and producing maps of one kind or another.  These might be represented as several different layers where each layer holds data about a particular kind of feature which is linked to a position on a map and a record in an attribute table.

GIS is much more than maps.  Users can query the data and present the answers in maps, tables and other graphic representations to virtually see the issues before them and then select the best course of action.