I want to produce one PNG image for each country in the world. The pixel colors come from a raster that describes the vegetation, and the boundaries of the countries come from a shapefile.

I managed to do almost all of it using the raster and rgdal libraries in R:

r <- raster('gm_lc_v3.tif')
p <- readOGR('ne_10m_admin_0_countries','ne_10m_admin_0_countries')
i <- 66 # Dominican Republic, a small country for fast example
country <- crop(r,p[i,]) # produces the rectangular crop below


m1 <- mask(country,p[i,]) # crops on the country boundary


m2 <- mask(country,p[i,],inverse=T) # crops outside the boundary


m2[m2 < 20] <- NA # turns all land into NA


What I need now is to combine the two rasters (m1 and m2) into a single raster, with all data from the country, and only land/water data from outside the country. Like this (made in Gimp):


I have tried all the following so far, but without success:

m3 <- cover(m1,m2)
m3 <- cover(m1,m2,identity=T)
m3 <- merge(m1,m2)
m3 <- overlay(m1,m2,fun=function(x,y){return(x+y)})
m3 <- mask(m1,m2)
m3 <- stack(m2,m1)

They return all black, or different colors from the original. What am I missing?

  • Try changing all your NA's to 0 (assuming no 0s in the grid) then just add them. – Badger Sep 15 '16 at 22:02

Use the function plot (look at the help from package raster) with the argument add = TRUE

plot(m2, col='black')
plot(m1, col=rev(terrain.colors(255)), box=FALSE, axes=FALSE, add = TRUE)

Or Try this

image(m2, add = TRUE, col = 'black')
| improve this answer | |
  • It doesn't work, with or without the 'col' parameter. – Rodrigo Aug 17 '16 at 13:53
  • Also tried using the 'alpha' parameter, but it didn't work. – Rodrigo Aug 17 '16 at 14:00
  • @Rodrigo In which way 'it doesn't work?' – nebi Aug 17 '16 at 14:57
  • With 'col' (like you used it), I got a big square over the (correctly merged) map. Without the 'col' parameter, the second plot simply erases the first (what's strange, because the 'add=T' is still there, and all the NAs really should have become transparent). – Rodrigo Aug 17 '16 at 15:04
  • @Rodrigo I updated the code. Better? – nebi Aug 17 '16 at 15:24

Worked with merge, only the colortable was missing:

m3 <- merge(m1,m2)
m3@legend@colortable <- m1@legend@colortable


m3 <- merge(m1,m2)
m3@legend <- m1@legend


| improve this answer | |
  • I think there must be a faster way to do it, though. – Rodrigo Aug 17 '16 at 16:24

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.