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;