On 14/03/2012 19:02, Rich Shepard wrote: > > I assume the reason is that the region is a square. Indeed. > What command could I pass to r.mapcalc that would clip > the raster map to the basins themselves Define a MASK before running r.mapcalc http://grass.osgeo.org/grass64/manuals/html64_user/r.mask.html Hermann