What is GIS?

Geographic Information Systems (GIS) are used in numerous disciplines in numerous ways and are therefore difficult to define. One way of tackling the beast is by basing the definition on what a GIS can do. The following offers an example of this kind of definition:

A GIS is a computer-based tool for mapping and analyzing geographic phenomena and events on Earth. With the help of a GIS the user can collect geographically referenced data (data input/acquisition), store it (data management), retrieve it, transform it (data manipulation and analysis), and finally display it in various formats to support decision making.

GIS organize data in layers. Each layer contains a specific type of information. The layers can be linked together for some pretty sophisticated types of analysis. Note that each layer contains a subset of information that would be present on a regular map.

Fig. 1.1 Layer representation in a GIS

What makes GIS technology unique is its ability to integrate geographic (spatial) and database (tabular, attribute data) information in each layer. Therefore, each layer contains both geographic information (where something is located) as well as attribute information (what is located at a specific location).

A GIS differs from an Information System in one essential way; A GIS uses geographically referenced data. "Geographically" is the key. A GIS differs from CAD, statistical packages, and computer mapping software in the following ways: computer mapping packages do not have analytical capabilities; CAD programs can't handle attribute data; statistical software packages can't handle geographic data. GIS looks at connections between activities or features based on geographic criteria. The essential capability of a GIS that distinguishes it from other software programs is its ability to analyze linked spatial and non-spatial data.

Therefore, GIS provide a very sophisticated way to combine all data that may be relevant to a project and make them available for interrelated analysis. (See also Why use GIS?)

For more information visit the GIS Primer at: http://www.innovativegis.com/basis/primer/primer.html