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I have an elevation model plotted in R

r <- raster("example.dem")
plot(r, col = topo.colors(20))

Elevation plot

Some of the values are below sea level (0), and I'd like to have those display in red. How can I assign specific ranges to specific colours in the plot()?

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37

Here is a really simple example

library(raster)
data(volcano)
volcanoR <- raster(volcano)

#making colors below 100 red and above 180 blue in this example

breakpoints <- c(94,100,120,140,160,180,195)
colors <- c("red","white","white","white","white","blue")
plot(volcanoR,breaks=breakpoints,col=colors)

enter image description here

You just need to pass the plot a vector of break points and a vector of colors to match the breakpoints. Check out the RColorbrewer package for some very nice built in color ramps. Also check out the classInt package for making the breakpoints.

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  • Excellent- embarrassing how long I fiddled with this. Is there a straightforward way to import colour ramps from colour brewer? EDIT: sorry, I now see you're referring to a package, not the site!
    – Simbamangu
    Nov 29, 2011 at 13:25
  • 3
    @Simbamangu, We have all been there. I actually find many of the examples of doing this obfuscate what is actually being passed as breakpoints and colors by using objects created from other packages (like the ones I suggest). I think it is simplest to see it like this, and then go on to use the other packages to create appropriate breakpoints and color ramps without doing so much work.
    – Andy W
    Nov 29, 2011 at 13:28
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    I completely agree with that - the examples in many of the R packages are really tough to figure out, with too much carried through from other objects!
    – Simbamangu
    Nov 30, 2011 at 6:39
  • What if you want to specify the colors of certain values, instead of intervals?
    – Rodrigo
    Apr 26, 2021 at 23:08
  • If you want the legend to look the same @Rodrigo, you can just make the interval very small and cover the value of interest. If you want to plot categories instead of continuous, see stackoverflow.com/a/19139384/604456 for an example. (Or you could use other plotting libraries, like ggplot.)
    – Andy W
    Apr 27, 2021 at 12:20

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