[R-sig-Geo] Subset polygon(s) from a country from wrld_simpl

[Lars Dalby]

Dear list

I am trying to make a subset of wrld_simpl to use as mask for a raster
layer.
I have a list of countries and I can do the subset quite easily. However I
would like to have one (or several) of the polygons from Russia in the list
also - Kaliningrad on the coast of the Baltic. This is where I run into
trouble.
How do I cut these out and subsequently subset wrld_simpl accordingly?

require('sp');require('maptools')

cntr <- c('Denmark', 'Germany', 'Norway', 'Ireland', 'United Kingdom',
'France', 'Italy', 'Sweden', 'Finland', 'Spain', 'Portugal', 'Latvia',
'Estonia', 'Slovenia', 'Belgium', 'Netherlands', 'Austria', 'Poland',
'Switzerland', 'Morocco', 'Algeria', 'Tunisia', 'Slovakia', 'Lithuania',
'Croatia', 'Czech Republic')

data(wrld_simpl)
NW <- wrld_simpl[which(wrld_simpl at data$NAME %in% cntr),] 

#I tried to use the overlay function, but that didn't quite do the trick:

rus <- wrld_simpl[which(wrld_simpl at data$NAME == 'Russia'),]

x <- 21.335449; y <- 54.788017 
P <- data.frame('x' = x, 'y' = y)
coordinates(P) <- ~x+y
ov <- overlay(P, rus)
ov # 1

# Now if I move the point further east and repeat:

x <- 90.335449; y <- 54.788017 
P <- data.frame('x' = x, 'y' = y)
coordinates(P) <- ~x+y
ov <- overlay(P, rus)
ov # still 1- so I guess this refers to the single object in the polygons
slot of rus, which is not quite what I'm after.

#sessionInfo()
R version 2.14.1 (2011-12-22)
Platform: x86_64-apple-darwin9.8.0/x86_64 (64-bit)

locale:
[1] C

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
[1] dismo_0.7-17    maptools_0.8-14 lattice_0.20-6  foreign_0.8-49 
[5] raster_1.9-70   sp_0.9-97       ncdf_1.6.6     

loaded via a namespace (and not attached):
[1] grid_2.14.1  tools_2.14.1


Any suggestions on how to solve this would be highly appreciated.

Best regards and Happy Easter!

Lars

Lars Dalby
Msc. PhD student
Ecoinformatics & Biodiversity
Department of Bioscience, Aarhus University
Denmark

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