GIS (geographic information system) contains data (information) and maps; and a computer interface ties them together to create a visualization tool. GIS is a method of representing, questioning, and analyzing geographic data and other pertinent data (known as relational data) on a computer screen.

A GIS consists of map information, a database, and a computer based link between them. Examples would include a street map, a phone book, and a computer interface. GIS creates a link between spatial and non-spatial data. GIS makes connections between activities based on geographical proximity. You can use GIS to examine the data spatially. This can then lead to insights, or explanations of phenomena.

How does a GIS work?

The power of a GIS comes from the ability to relate different information in a spatial context and to reach a conclusion about this relationship. Most of the information we have about our world contains a location reference, placing that information at some point on the globe. When rainfall information is collected, it is important to know where the rainfall is located. This is done by using a location reference system, such as longitude and latitude, and perhaps elevation. Comparing the rainfall information with other information, such as the location of marshes across the landscape, may show that certain marshes receive little rainfall. This fact may indicate that these marshes are likely to dry up, and this inference can help us make the most appropriate decisions about how humans should interact with the marsh. A GIS, therefore, can reveal important new information that leads to better decisionmaking.

Many computer databases that can be directly entered into a GIS are being produced by Federal, State, tribal, and local governments, private companies, academia, and nonprofit organizations. Different kinds of data in map form can be entered into a GIS. A GIS can also convert existing digital information, which may not yet be in map form, into forms it can recognize and use. For example, digital satellite images can be analyzed to produce a map of digital information about land use and land cover . Likewise, census or hydrologic tabular data can be converted to a maplike form and serve as layers of thematic information in a GIS.