I'm currently analyzing the change detection for urban expansion over a decade starting from 2006-2016.

How can I use raster calculator in order to know the changes?

For example, from agriculture to urban area and etc. I already classified the images into 4 classes, urban area,vegetation,water bodies and barren land.

  • 1
    What software are you using?
    – Fezter
    Commented Nov 30, 2016 at 5:46
  • What's your goal? To identify where there were changes, or to be able to discern from a single output what the particular changes were?
    – J Kelly
    Commented Dec 29, 2016 at 1:45

1 Answer 1


Try reclassifying the rasters to a different scale of numbers, such as

urban = 1
ag = 10
forest = 100
water = 1000

Then just subtract the rasters in Raster Calculator:

0 will mean unchanged.
9 will mean ag --> urban
-9 will mean urban --> ag
99 will mean forest --> urban
90 will mean forest --> ag
-99 will mean urban --> forest etc.

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