Using Spatial Data with SAS/GIS Software

Assessing Your Spatial Data Needs

You use a geographic information system when you want to explore data in the context of a map, so you must have a map in order to use SAS/GIS software. Further, the map must be in the form of spatial data that SAS/GIS software can use.

Assessing Your Attribute Data

The first step in deciding what spatial data you need is to assess the attribute data that you want to analyze. Obviously, the attribute data must have a spatial component. That is, the data must contain at least one variable with values that relate to location. Examples include city, state, or country names or codes; street names; addresses; and so forth. Since SAS/GIS software is part of the SAS System, the attribute data must also be in the form of a SAS data set or SAS view. You can use any method that is available for transforming your attribute data into a SAS data set or SAS view, if it is not already stored in one of those formats. These methods include, but are not limited to

Using SAS DATA steps or the SAS Import Wizard for reading external files into SAS data sets
Using SAS/ACCESS software or the SQL procedure for creating views to database files
Using SAS DATA steps or the SQL procedure to create dynamic views to SAS data sets.

Determining Your Spatial Data Requirements

In order to analyze the attribute data with SAS/GIS software, you need spatial data that contain representations of features to at least the same level of detail as the location information in your attribute data. For example, if your attribute data consist of demographic data for states, then your spatial data must provide at least state boundaries. If your attribute data consist of demographic data for smaller census tracts, then you need spatial data containing the corresponding census tract boundaries in order to explore the demographic data with SAS/GIS software.

Locating a Source of Spatial Data

You may be able to purchase appropriate spatial data that have already been prepared in SAS/GIS format by a commercial data vendor. Contact SAS Institute Technical Support for information on sources for spatial data in SAS/GIS format.

The other way to acquire spatial data for use with SAS/GIS software is to import it from other formats. One readily accessible source of maps for importing is the map data sets that are provided with SAS/GRAPH software, although these maps provide only political boundaries and not other physical features such as rivers or major highways. Other sources for spatial data that you can import include the following:

Governmental agencies. For example, SAS/GIS software can import spatial data from TIGER Line files produced by the U.S. Census Bureau and from DLG files produced by the U.S. Geological Survey.
Drawing and computer-aided design (CAD) packages. SAS/GIS software can import the DXF interchange format that is supported by products from various vendors.
Dynamap files from Geographic Data Technology, Inc. (GDT).
MapInfo .MIF and .MID files.
Uncompressed ARC/INFO transport files from ARC/INFO Software by Environmental Systems Research, Inc. (ESRI).
User-created files. If no other source is available, you can use SAS DATA steps to process your spatial data into the required generic format, which SAS/GIS software can then import.

Whatever the source, the spatial data must have at least one variable with values that match values in the attribute data that you want to analyze. If necessary, you can use the SAS System to process either the attribute data or the spatial data. For example, if your attribute data contain state names and your spatial data contain state codes, you can use SAS DATA steps to generate corresponding codes for the names. Likewise, if your attribute data and spatial data both have variables that contain codes to identify areas in the map, but the two sets of data use different codes for the same areas, then you can use SAS DATA steps to translate the coding schemes.

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