# "getCountries" code taken from:
# http://stackoverflow.com/questions/5126745/gadm-maps-cross-country-comparision-graphics

# Load required libraries
library(sp)

# Load file from GADM
# Specify the countries for fileName using ISO3C
# like "AFG" for Afghanistan.
# "level" specifies adminsitrative level.
loadGADM<-function(fileName,level=0,...){
    load(url(paste("http://gadm.org/data/rda/",fileName,"_adm",level,".RData",sep = "")))
    gadm
}

# Add prefix (ISO3C code) to shapefile.
changeGADMPrefix<-function(GADM, prefix) {
    GADM <- spChFIDs(GADM, paste(prefix, row.names(GADM), sep = "_"))
    GADM
}

# Load file and change prefix
loadChangePrefix<-function (fileName, level = 0, ...) {
    theFile <- loadGADM(fileName, level)
    theFile <- changeGADMPrefix(theFile, fileName)
    theFile
}

# Apply all the functions:
getCountries <- function (fileNames, level = 0, ...) {
    polygon <- sapply(fileNames, loadChangePrefix, level)
    polyMap <- do.call("rbind", polygon)
    polyMap
}


## Example

countries<-c("CZE","DEU","AUT","SVK","POL")
EUR<-getCountries(countries,level=1) # Level 1
CZE<-subset(EUR,ISO=="CZE")
plot(EUR)
plot(CZE,col="steelblue4",add=T)