[R] R equiv to proc gremove in maps package

[Barry Rowlingson]

Fred Rohde wrote:
> 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.

  This sounds like the standard GIS 'dissolve' function. Its probably a 
bad idea to try and give R all the GIS functions on the planet - better 
to link it with a GIS and use that instead.

  GRASS-GIS can do a dissolve operation, using v.reclass with the -d 
option. See http://grass.itc.it/gdp/html_grass5/html/v.reclass.html

  Of course you'll then need some way of getting your data into and out 
of GRASS, there's a GRASS R library by Roger Bivand that might help and 
an R-Arc/Info lib by Virgilio Gomez-Rubio that also might help.

  Doing it from R's 'maps' format could be fun though... for some 
definition of 'fun'...

Barry