In
the following example, the shapefile is a ZCTA file from the US Census Bureau
that contain polygons that are based on ZIP codes. The ZCTA field is the identifier
that you want to use, but the polygons in the shapefile do not have unique
values for ZCTA. If you do not specify the ID statement, then the GMAP procedure
draws extra lines between the map areas for ZCTA.
By identifying the ZCTA field in the ID statement, you ensure that the
polygons for each value of ZCTA are grouped together and assigned different
SEGMENT values in the output map data set. The GMAP procedure can now draw
the map areas for ZCTA correctly.
proc mapimport out=myzcta datafile="c:\zt06_d00.shp";
id zcta;
run;
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