plotting raster data in R: adjusting the labels and colors of a classified raster

August 2, 2012

(This article was first published on geo-affine » R, and kindly contributed to R-bloggers)

Thank’s to Andrej who wrote this comment:
“Is it possible to to color the resulting 12 clusters within your original image to get a feel for visual separation?”
You can do so:

map in R with labels

map in R with labels (click to enlarge)

arg <- list(at=seq(1,12,1), labels=c("none","none","vegetation","none","none","vegetation","none","none","none","none","water","none")) #these are the class names
color=c("black","black","green","black","black","green","black","black","black","black","blue","black") #and color representation
plot(G, col=color, axis.arg=arg)

But how to get values at a location? You will need these values to determine whether the defined class is representing a water body or a forest. Use the layerstack in a second plot as reference. But use this line to determine the class number at a chosen location:

extract(G, data.frame(locator()))

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