[R-sig-Geo] how to transform Polygons to SpatialPolygons

[Hans-Jörg Bibiko]

On Jun 22, 2010, at 10:29 PM, Weidong Gu wrote:

> 
> The question is how to transform 'mainland' back into SpatialPolygons format. 


Hi,

maybe try the following:

library(maps)
library(maptools)
usa=map('usa',plot=F,fill=T)
IDs=sapply(strsplit(usa$names,':'), function(x) x[1])
crs=CRS('+proj=longlat +ellps=WGS84')
sp.usa=map2SpatialPolygons(usa,IDs=usa$names,proj4string=crs)

mainland <- list(slot(sp.usa,'polygons')[[3]])
sp_mainland <- SpatialPolygons(mainland, proj4string=crs)
str(sp_mainland)
plot(sp_mainland)

Cheers,
--Hans


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Hans-Joerg Bibiko
Max Planck Institute for Evolutionary Anthropology
Department of Linguistics
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