[R-sig-Geo] how to calculate areas of shape files using R
r.hijmans at gmail.com
Tue Feb 1 08:58:11 CET 2011
> A small caveat - if the coordinates are planar, the explanation holds, if
> geographical (degrees), it doesn't. The naive area values have been used
> internally to plot larger Polygon objects before smaller Polygon objects,
> to avoid overplotting in earlier versions of R that did not "identify"
> holes automatically. So first make sure that you have planar coordinates,
> otherwise the "area" values have no metric. If need be, project with
> spTransform() methods in rgdal
If the coordinates are spherical (in degrees) you can compute the area of
polygons in a SpatialPolygons* object like this:
View this message in context: http://r-sig-geo.2731867.n2.nabble.com/how-to-calculate-areas-of-shape-files-using-R-tp5975749p5980100.html
Sent from the R-sig-geo mailing list archive at Nabble.com.
More information about the R-sig-Geo