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I want to create a rule for applying a particular symbology to a raster in QGIS. I do not know if this is possible. In detail, I would like to classify (as discrete) values of a raster1 based on its values and those of another raster (raster2). Both rasters are completely overlapping.

As an example, I want pixels colored in green when values of raster2 are 1 and values of raster1 are <= 5 otherwise pixels must be in red; similarly when values of raster2 are 2 and values of raster1 are <=1.5 color pixels in green otherwise in red; etc.

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  1. Use Raster Calculator to create a new (binary) raster based on the conditions you have with the following expression that creates a value 1 if one of the conditions is fulfilled (green) or 0 (red) if none of the conditions is fulfilled. You can add more lines for your further conditions:

    "raster2@1" = 1 and "raster1@1" <=5 or
    "raster2@1" = 2 and "raster1@1" <=1.5
    
  2. The resulting raster has values of 0 or 1. Set this raster's color to Singleband pseudocolor (see screenshot) and use a color ramp from red to green.

By the way: red/green colors can be problematic due to color blindness issues, see e.g.:

It’s important to emphasize here that using red and green, while intuitive, should be avoided. https://seaborn.pydata.org/tutorial/color_palettes.html

Resulting raster, clicked a green pixel (value=1, color=green) with underlaying raster1=1.33883 and raster2=1: enter image description here

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    Just a correction. It doesn't work with the formulation you posted. I have changed it: IF(("raster2@1" = 1) and ("raster1@1" <=5)) or IF(("raster2@1" = 2) and ("raster1@1" <=1.5))
    – AUS85
    Commented Jan 23 at 12:56

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