I have a raster DEM and a polygon covering a part of it. I need an area-elevation distribution (i.e. how many m2 are in which elevation interval). 20m intervals will be fine. I can't figure it out.
- Generate contours at the desired intervals from your DEM and use the lines to cut up your polygon.
- Clip your DEM using your polygon, then reclassify the DEM using the desired interval ranges, followed by a little math - get the number of pixels in each class times the area of a pixel. (See Measuring area of raster classes? which discusses ArcGIS tools, but the methods would be the same.)
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