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I want to calculate the aspect and slope for polygons, because they appear as fruit-growing areas.

I got the DEM 1m for my datas and calculated aspect and slope with the QGIS functions. Then I reclassed the new rasterdata as table and made categories from 1-3 with defined valued for both aspect and slope.

Lastly, I merged the two reclassed raster layer together, to create a combined aspect and slope Layer.

The problem is, that a value of 3 can be created out of value 2 of aspect and 1 of slope and vice versa.

This is kind of Interpretation cause the values are ranges.

Is there a way to calculate aspect and slope mor detailed for a polygon?

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  • You can multiply one of them by 10 before adding them. Then you end up with values 12 or 21, rather than both 3. For example, if you multiplied slope by 10, your unique values will be 11, 21, 31, 12, 22, 32, 13, 23, 33 where the first digit represents aspect and the second is slope.
    – Matt
    Commented Oct 19, 2022 at 20:47
  • Thanks for your respond matt! Do i multiply one of the reclassed layers in the rastercalculator? By adding my layer, add the multiply symbol and then 10?
    – Micha
    Commented Oct 19, 2022 at 21:01
  • Indeed, you can multiply one and add both together in the same expression. Something like slope * 10 + aspect. I realised I got the raster the wrong way round in my previous comment. Slope will be the first digit and aspect the second :)
    – Matt
    Commented Oct 20, 2022 at 5:48
  • Thank you Matt, i was not aware if the fact that i could do such a simple thing! This will help me for sure! Kind regards Michael :)
    – Micha
    Commented Oct 20, 2022 at 7:15

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