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I have two raster maps (source: http://ghsl.jrc.ec.europa.eu/ghs_pop.php), one is with data from 1975, one is with data from 2015.

I want to substract the value of each individual pixel from the map of 2015 with each individual pixel from the map of 1975. That will get me the difference in population for each pixel.

How do I do this?

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You can use r.mapcalc. In the GUI just insert both maps substracting. Or from the console write:

r.mapcalc expression="output = 2015@yourdataset - 1975@yourdataset"

Just change the names of the rasters according to yours.

  • I already had the mapcalc window open, but it didn't seem like I could add more than one map... I feel stupid now. This is the correct answer, thank you – Necrophades Jan 30 '18 at 17:39

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