Joe, The "areaPolygon" function in the "geosphere" package can do this.
Robert On Fri, Sep 3, 2010 at 3:30 PM, <brwin...@aol.com> wrote: > > Good Afternoon > Does any one know of a package/function that could be used to compute the > square kilometers for polygons in a long-lat projected shapefile? > I can access the values in the "area" slots in the object resulting from > using maptool's "readShapePoly" command. I have approximated the km^2 from > these values by using one of the polygons's (such as a given state's) known > area in km^2 and rescaling the polygon's "area" relative to the state's known > area. I then applied this "scaling factor" to the other polygons in my > shapefile object to approximate the other polygons' are in km^2. > > However, if I understand things correctly, my approximate "area to km^2" > scaling will become increasing distorted as I move north or south relative > to my original "normalizing" state. Is there a function that can compensate > for changes in latitude when computing the polygon areas associated with > long-lat polygons? I hope this question is somewhat coherent > Thanks > Joe > > > > > [[alternative HTML version deleted]] > > _______________________________________________ > R-sig-Geo mailing list > R-sig-Geo@stat.math.ethz.ch > https://stat.ethz.ch/mailman/listinfo/r-sig-geo > _______________________________________________ R-sig-Geo mailing list R-sig-Geo@stat.math.ethz.ch https://stat.ethz.ch/mailman/listinfo/r-sig-geo
