Geographic Information Systems (GIS) is a technology that is used to view and analyze data from a geographic, or spatial, perspective. GIS links location to information, such as people to addresses, buildings to parcels, or streets within a network, and layers that information to give you a better understanding of how it all interrelates. You choose what layers to combine based on your purpose.

A GIS is most often associated with maps. A map, however, is only one of three ways a GIS can be used to work with geographic information. These three ways are:

• The Database View: a unique kind of database of the world - a geographic database, or geodatabase.
• The Map View: set of intelligent maps and other views that show features and feature relationships on the earth’s surface. Maps of the underlying geographic information can be constructed and used as "windows into the database" to support queries, analysis, and editing of the information.
• The Model View: a set of information transformation tools that derive new geographic datasets from existing datasets. These geoprocessing functions take information from existing datasets, apply analytic functions and write results into new derived datasets.

What Can You Do With GIS?

Map Where Things Are

• Find places that have the features you’re looking for and see where to take action.
• Find a feature to see where or what an individual feature is.
• Find patterns by looking at the distribution of features on the map instead of just an individual feature to see patterns emerge.

Map Quantities

People map quantities, like where the most and least are, to find places that meet their criteria and take action, or to see the relationships between places. This gives an additional level of information beyond simply mapping the locations of features. For example, a catalog company selling children’s clothes would want to find ZIP codes not only around their store, but those ZIP codes with many young families with relatively high income. Or, public health officials might not only want to map physicians, but also map the numbers of physicians per one thousand people in each census tract to see which areas are adequately served, and which are not.

Map Densities

While you can see concentrations by simply mapping the locations of features, in areas with many features it may be difficult to see which areas have a higher concentration than others. A density map lets you measure the number of features using a uniform area unit, such as acres or square miles, so you can clearly see the distribution.

Mapping density is especially useful when mapping areas, such as census tracts or counties, which vary greatly in size. On maps showing the number of people per census tract, the larger tracts might have more people than smaller ones. But some smaller tracts might have more people per square mile-a higher density.

Find What’s Inside

Use GIS to monitor what’s happening and to take specific action by mapping what’s inside a specific area. For example, a district attorney would monitor drug-related arrests to find out if an arrest is within one thousand feet of a school.  If it is, stiffer penalties apply.

Find What’s Nearby

Find out what’s occurring within a set distance of a feature by mapping what’s nearby.

Map Changes

Map the change in an area to anticipate future conditions, decide on a course of action, or to evaluate the results of an action or policy. By mapping where and how things move over a period of time, you can gain insight into how they behave. For example, a meteorologist might study the paths of hurricanes to predict where and when they might occur in the future.

Map changes to anticipate future needs. For example, a police chief might study how crime patterns change from month to month to help decide where officers should be assigned. Map conditions before and after an action or event to see the impact. A retail analyst might map the change in store sales before and after a regional ad campaign to see where the ads were most effective.

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