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I am looking for help for my master thesis. I have two layers, a set of households and burned area (vector data). I created buffer zones around each household and now want to estimate the burned area within a buffer. Unfortunately "intersect" doesn't help and always gives me the error code 506 - Object (506) has invalid geometry.

enter

I am working in QGIS 3.4.

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    Try fixing your geometries first: search for check validity and fix geometries in the processing toolbox – MrXsquared Jan 18 '20 at 15:25
  • Thanks, I now created a new layer through intersect. What's next? I still have different values for each pixel (day of burn) in my burned area but only want to calculate the total area burned within the buffer – Ida JAKOB Jan 18 '20 at 17:34
  • "for each pixel" - sorry i am confused. I thougt you have vector data? – MrXsquared Jan 18 '20 at 17:50
  • Yes, sorry. It is not each pixel but I don't know how to explain it properly. The layer shows different days during the year as "fields". Maybe the picture might help. I want to calculate the whole yellow area. – Ida JAKOB Jan 18 '20 at 18:00
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You can open the attribute table of your intersection layer and create a new double or integer field and enter the expression sum($area). This will sum up all areas of all features of that layer in the CRS units (so make sure your layer is projected to a metric system, then the result will be in m²).

If you want to sum the areas up by groups, use the expression sum($area, group_by:="buffer_id") where "buffer_id" refers to a fieldname which is unique within each buffer.

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  • Okay I did that, but how can I know calculate the area only within one buffer. I need an output like: 5000ha/m^2 in buffer 1. – Ida JAKOB Jan 19 '20 at 11:43
  • @IdaJAKOB see my edit – MrXsquared Jan 19 '20 at 11:48

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