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I am using QGIS 2.8.3. I started by classifying my area into habitat types using the semi-automatic classification plugin (SCP). Then I added points, and a 4m buffer around the points. So I could then clip the results of the SCP by the 4m buffer, to figure out what the habitat types are within the 4m buffer. Now I want to know the area or percentage cover of each habitat type for each point within the 4m buffer based on the SCP classification. Any ideas on the best way to do this?

Ayla
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  • The problem with clipping a raster with a vector is part cells are either included or omitted which can really mess with your counts. I would do this as a vector (raster to polygon, then clip polygon) and summarize. There are some summary plugins but it might be better to clip to a shapefile and open the DBF in Excel (or similar) and do your calculations there. – Michael Stimson Sep 07 '15 at 01:58
  • I have attempted this, but I dont know if maybe the file is just massive but when I try raster to polygon it computes for a long time, its been going for about an hour and no output yet? – Ayla Sep 07 '15 at 03:32
  • How many cells is it? What method are you using? Being classified data the conversion should dissolve internal boundaries but depending on how complex the data is it could take a long time. Perhaps you will need to extract by the buffer extent, convert to polygons and then clip, this would be best done in a python process but can be done manually. – Michael Stimson Sep 07 '15 at 03:49
  • ~3000 cells. Raster -> Conversion -> Raster to Vector – Ayla Sep 07 '15 at 04:17
  • is that 3k in one dimension or 30 x 100 = 3000? A small raster shouldn't take too long as long as it's not overly complex. I have performed this operation on 144k by 90k rasters without too much stress - but that was a condition raster (0/1) containing 9 areas of 0 and the remainder 1 which simplified well. Try subsetting the raster around a cluster of points or a single point as an example. To calculate percentage you need to calculate the area of the clip geometry and the clipped sections, have a read of http://gis.stackexchange.com/questions/23355/how-to-calculate-polygon-areas-in-qgis – Michael Stimson Sep 07 '15 at 04:30

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