A Geographic Information System, or GIS, consists of software and hardware which incorporate data in order to hold, analyze and display information concerning specific geographic regions. Local county governments in the United States typically provide an online GIS with data relevant to the county.
In short, a GIS is a digital map with various layers that represent different data sets. Google Maps and Google Earth are two common examples of Geographic Information Systems. Both products include several layers of data by default, and additional data layers can be added.
The amount and types of data that a specific GIS deals with can vary considerably and depend on the application. Such is the case for a county's GIS. Whereas a county with many industrial plants might incorporate a data layer displaying pollution-emitting sites, a rural county would lack such information; and, conversely, a rural county with lots of agriculture may display acres of specific crops planted.
As an example, Ventura County in California integrates its GIS into Google Maps – layering its data onto Google's cartography and satellite imagery. Among the many data layers available with the Ventura County GIS are: parcel labels, county libraries, election precincts, land use, political districts, school districts and special districts. To locate a county GIS, a Google search including the county name and "GIS" often yields a direct link to the page. Otherwise, visit the website of the county in question and follow the appropriate links.