SAS/GIS software provides an interactive Geographic Information System (GIS) within the SAS System. A Geographic Information System is a tool that allows you to organize and analyze data that can be referenced spatially--that is, data that can be tied to a physical location. Many types of data have a spatial aspect, including demographics, marketing surveys, and epidemiological studies.

This software also enables you to do more than simply view data in its spatial context. It allows you to interact with data by selecting features and performing actions based on those selections. SAS/GIS software draws on computing capabilities of the SAS System and enables you to access, manage, analyze, and present your data easily.

SAS/GIS software uses two basic types of data:

1. Spatial data - containing the coordinates and identifying information describing the map itself
2. Attribute data - containing information that can be linked to the spatial data--for example, matching addresses or coordinates in the spatial data

For example, the U.S. Census Bureau distributes both types of data:

• TIGER line files - contain spatial information that you can use to build maps.
• summary tape files - contain population and other demographic information that you can link to the maps.

Spatial Data

Spatial data contain the coordinates and identifying information for various map features. Three types of features can be represented in the map: points, lines, and areas. The various physical aspects of the map--political boundaries, roads, railroads, waterways, and so forth--are organized into layers according to their common features.

For example, the collection of points that represent park locations can be organized into a parks layer, the collection of lines that represent streets can be organized into a streets layer, and the collection of areas that represent census tracts can be organized into a tracts layer.

A layer can be either static or thematic. Static layers use the same graphical attributes (color, line width, and so forth) for all features in a layer. Thematic layers can use different graphical attributes to classify the features in the layer. For example, a thematic area layer representing sales regions could use different colors to show the quarterly sales performance of each region. A thematic line layer representing highways could use different line widths to show the classes of roads.

Attribute Data

The second type of data used in a GIS is attribute data. With SAS/GIS software, SAS data sets or data views can be associated with the map through links to the spatial data. For instance, the spatial data might represent a county and contain information for city boundaries, census tract boundaries, streets, and so forth. An attribute data set with population information for each census tract can be linked to a map by the corresponding tract value in the spatial data.

Two of the ways in which you can use attribute data in SAS/GIS include:

• using variables from the attribute data as themes for layers. For example, an attribute data set containing population data could provide a theme for a map of census tracts.
• creating actions that display or manipulate the attribute data when features are selected in the map. The actions can range from simple, such as displaying observations from an attribute data set that relate to features in the map, to complex, such as submitting procedures from SAS/STAT software to perform statistical analyses.

Interacting with Your Data

One of the key concepts with SAS/GIS software is selecting features from the map and then performing actions on the attribute data associated with those features. Actions can be defined to:

• display observations from the attribute data sets that relate to the selected map features
• open additional maps that relate to selected map features
• display graphic images that relate to the selected map features
• interactively subset the attribute data sets according to the subset of selected map features, and
• submit SAS programs for processing subsets of the attribute data that relate to the selected map features.