Plot UK choropleth maps developed using LA and ETS data but can be applied more generally

map_tb.R

map.tb <- function(map.data, g=NA, brks=NA, title="", value="tb", file=FALSE){
  ## plot UK choropleth maps
  ## developed using LA and ETS data but 
  ## can be applied more generally
  ##
  ## map.data: map object loaded by readOGR()
  ## g: number of groups for values; max(g)=9
  ## brks: given break points to group values
  ## title: plot title
  ## value: variable name of colouring value (string)
  ## file: output to file (logical)
  
  if(file){png(file=paste("figures/", title, ".png", sep=""), width = 600, height= 550)}
  
  par(mfrow=c(1,1))
  par(mar=c(0.1, 0.1, 1.5, 1.5))
  
  if(!is.na(brks)){
    ## defined breakpoints
    cols <- brewer.pal(length(brks), "Greens")
    frac <- cut(map.data@data[,value], brks)
    gs <- cols[findInterval(map.data@data[,value], vec = brks)]
    plot(map.data, col = gs)
    legend("topright", legend = levels(frac), fill = cols, title=title)
  }
  else if(!is.na(g)){
    ## defined number of groups
    cols <- brewer.pal(g, "Greens")
    frac <- cut2(map.data@data[,value], g=g)
    gs <- cols[as.integer(factor(frac))]
    plot(map.data, col = gs)
    legend("topright", legend = levels(frac), fill = cols, title=title) 
  }
  
  if(file){dev.off()}

}