Geographic Information Systems (GIS)
GIS is best understood when thought of in terms of maps. Maps are graphical depictions of the surface features of land drawn to scale. They detail spatial data, such as the location of a roadway or the length of a river, in a static, printed format. GIS integrates many layers of geographic data in a computer and provides a framework to dynamically manage, overlay, analyze, and illustrate the attributes and patterns of the geographic data.
GIS analysis is based on spatial data. Spatial data are people, places, or things that have a geographic component. Examples of common geographic components include street addresses, property parcel tax ID numbers, zip codes, city boundaries, or national borders.
Data in a GIS is spatially-referenced based on its geographic component and therefore can be overlaid with other geographic data. The graphic below illustrates the concept of layering geographic data. Individually, each layer of data reveals a limited amount of information, but when superimposed, the composite reveals great complexity.
In addition to a geographic component, GIS data also contains attribute information. Attribute information describes the people, places, or things that make up the built and natural environment. A house has a street address that details its geographic location, but there are also additional pieces of non-geographic information, or attributes, that describe the home.Examples of attribute information about a house include the year it was built, the price of the home, and the size of the home. The power of GIS lies in its ability to accurately pinpoint the geographic location of a feature and associate attribute information about the feature. In the housing example, we can use the GIS to answer questions such as, “How many houses within a mile of my house were sold for more the $200,000 in the past year?”