Using Spatial Data with SAS/GIS Software

Hints and Tips

When SAS/GIS uses a nonuniversal coverage, that is, one in which the value of the WHERE clause is not '1', to subset a map, all of the layers in the map must also satisfy this WHERE clause. If any of the layers do not satisfy this WHERE clause, some features of the map may not be displayed, and the reason may not be apparent.
For example, if you have a map of the United States and you want to create a subset map containing just North Carolina and Virginia, you could use the following COVERAGE statement to create the subset map:
```
COVERAGE CREATE NCVA /
    where='STATEL IN(37 51) OR
           STATER IN(37 51)';
```
Any points or lines that do not have 37 or 51 as the STATEL or STATER value will not display on the map.
Defining a layer with WHERE='1' displays all of the features in the underlying spatial data that have that type. For example, if you have a map with a point layer that contains capital cities, and you add a new point layer for grocery store locations by using WHERE='1' for the layer definition, the grocery store layer will display all of the point features in the spatial data. This layer includes capital cities, grocery stores, and all other point features in the spatial data.
You may find this confusing if you are not aware that all point features are being displayed when you intend to display only one layer.
You may encounter this situation because the GENPOINT import, by default, defines all point layers with a WHERE='1' clause. You can use the Modify layers button on the GIS Spatial Data Importing window to redefine the layer definition to be a WHERE clause that uniquely identifies the set of points in the layer. If the layer already exists on the map, you can use the LAYER statement in PROC GIS to redefine the layer with a WHERE clause that defines only those points in the layer.

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