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I’ve got maps of fish farms which I think might be relevant for my species distribution mode. However these maps are essentially just polygons drawn over individual fish cages. I’ve also got data on aquatic vegetation, depth, etc. which are in raster format. I want to make a new raster from the fish farm polygons, with the same extent and pixel size as the ones for the depth etc., but which includes, as a value in each pixel, the percent of the area which is covered by the polygons. So that if 15% of the area of the pixel was a polygon, the pixel would have a value of .15, if no fish farms were in that pixel, it would have a value of 0, etc.

How would I go about doing this using QGIS?

So far I’ve tried to rasterise the polygons, but that ends up with having rasters where the polygons were with rather odd values on them whose provenance is unknown to me.

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    The raster model doesn't really support the idea of partial overlap (either it does, or it doesn't), so you're looking at vector processing of pixels (which is ugly, from a scale perspective).
    – Vince
    Commented Jul 22, 2023 at 10:35
  • In QGIS you can create a polygon grid ("fishnet") with same cell size as your raster pixels. Intersect the fishnet and fish farms. Calculate area of each intersection as an attribute and divide that by area of a pixel/cell (for proportion or multiply by 100 for percentage). Rasterize the intersections using proportion or percentage as the cell value.
    – user2856
    Commented Jul 22, 2023 at 11:07
  • If you can settle for whole percentage, you can oversample by 100 (1/10 pixel size), then mask and sum (it's still going to impact processing speed).
    – Vince
    Commented Jul 22, 2023 at 12:23

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