Is there an R equivalent to SAS's proc gremove?  You would use this procedure to combine the units on an existing map, for example to build a map of Metropolitan Statistical Areas (MSAs) from the [US] counties dataset where the internal boundries surround the MSAs (which are groups of counties) rather than the individual counties.  I can imagine the mechanism would be to find and erase the boundries within each group.  Is there a way to do that in R?  I looked at the S reference on building geographical databases, and I could probably fumble through the C code to build the binary files of lines and polygons, but have no idea how to implement the shell program to extract the datapoints.  Thanks.



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