How to clip WorldMap with polygon in R?

Question

I have imported a world map dataset from www.GADM.org using the R package raster. I would like to clip it to a polygon I create to reduce the size of the map. I can retrieve

Answer 1

How about a little intermediate step? I adopted the following code mainly from R-sig-Geo and I think it should do the trick. You'll need both 'maptools' and 'PBSmapping' packages, so make sure you've got them installed. Here's my code:

# Required packages
library(raster)
library(maptools)
library(PBSmapping)

# Download world map
WorldMap <- getData('countries')
# Convert SpatialPolygons to class 'PolySet'
WorldMap.ps <- SpatialPolygons2PolySet(WorldMap)
# Clip 'PolySet' by given extent
WorldMap.ps.clipped <- clipPolys(WorldMap.ps, xlim = c(-20, 40), ylim = c(30, 72))
# Convert clipped 'PolySet' back to SpatialPolygons
EuropeMap <- PolySet2SpatialPolygons(WorldMap.ps.clipped, close_polys=TRUE)

I just tested it and it worked without any problems. It took some computation time to transform SpatialPolygons to PolySet, though.

Cheers, Florian