A Geographic Information System (GIS) is a computer system that provides geographic information to support decision making. Similar to other information systems, it offers functions to input, manage, retrieve, analyze, and output data.

A GIS is unique in that geographic data are rather different from traditional data used in business and similar applications. Most geographic data are multidimensional. For example, it takes at least two coordinates to specify a location. When height is involved, a point becomes three dimensional. Moreover, geographic objects might change with time. The addition of this temporal parameter makes geographic objects four dimensional.

The unique characteristics of geographic data require specialized functions which are not normally provided by traditional Database Management Systems (DBMS). Among them are cartographic functions, geographic analysis, and geographic modeling.

Cartographic functions are important to human interface design in a GIS. We often interact with a GIS through a map display and visualize geographic data in graphic forms.
Geographic analyses, such as finding the quickest route from one city to another, are more complex than most of the statistical functions found in DBMS.

Geographic modeling, the ultimate tool in supporting decision making by allowing us to simulate real world situations, is highly specialized. This kind of modeling, such as predicting the effect of an oil spill, is particularly useful when a corresponding real life undertaking is prohibitively expensive or risky.

Although GIS are very different from DBMS, data management is an important module of a GIS since the operation of an information system depends heavily on the availability of data. Hence many GIS, such as Arc/Info, Intergraph, Vision and CARIS do incorporate off-the-shelf DBMS as part of their systems. This is mainly to reduce the development cost of the GIS software.