The input map data set must be a map data set and contain these variables:
It also can contain
Any other variables in the input map data set do not affect the GREDUCE procedure.
If you are using map data sets in which area boundaries do not match precisely (for example, if the boundaries were digitized with a different set of points), PROC GREDUCE will not be able to identify
common boundaries properly, and this results in abnormalities in your maps. These abnormalities include mismatched borders, missing vertex points, stray lines, gaps, and distorted
polygons.
If the points in the area boundaries match up except for precision differences, round each X and Y value in your map data set accordingly, using the DATA step function ROUND before using PROC GREDUCE.
(See SAS Language Reference: Dictionary for information on the ROUND function.)
For example, if the map data set APPROX has horizontal and vertical coordinate
values for interior boundaries of unit areas that are exactly equal only to three decimal places, then this DATA step creates a new map data set, EXACT, that will be better suited for use with PROC
GREDUCE:
data exact;
set approx;
if x ne . then x=round(x,.001);
if y ne . then y=round(y,.001);
run;
See About Map Data Sets for additional information on map data sets.
Copyright © 1999 by SAS Institute Inc., Cary, NC, USA. All rights reserved.
