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 GREMOVE will not be able to identify common boundaries properly, resulting in abnormalities in your output data set.

If the points in the area boundaries match up except for precision differences, before using PROC GREMOVE round each X and Y value in your map data set accordingly, using the DATA step function ROUND. See SAS Functions and CALL Routines: Reference for information about the ROUND function.

For example, if you have a map data set named APPROX in which the horizontal and vertical coordinate values for interior boundaries of unit areas are exactly equal only to three decimal places, this DATA step creates a new map data set, EXACT, that is better suited for use with the GREMOVE procedure:

data exact;
   set approx;
   if x ne . then x=round(x,.001);
   if y ne . then y=round(y,.001);
run;

You can also use the FUZZ option to specify a level of tolerance so that the boundaries do not need to match precisely.