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I have a set of polygons, several of which overlap. I want to process them so that (in the simplest case) two overlapping polygons become three non-overlapping polygons.

I can split up the polygons using the the Intersection tool, but this leaves me with the two original (and still overlapping) polygons, plus two new polygons corresponding to the overlap of each of the originals.

It feels like this should be a common enough task that there would be a built-in tool for it, but if so I can't find it.

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Try using 'Polygon self-intersection' in the processing toolbox > SAGA-tools > Vector polygon tools. This function is implemented at least since QGis 2.14.15. Before:

Overlapping features before processing.

It will do exactly what you want. All overlapping areas will be removed and replaced by a new geometry. The formerly overlapping parts will recieve concatenated field values. After:

New features after processing with new concatenated field value

  • That's great, thanks. There are so many tools hidden away! – user2980115 Jun 8 '17 at 13:13
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Use processing tools v.clean and delete identical geometry from Grass toolsets.

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There might be easier solution but here is what I would do: you can get the intersection polygon with intersection polygon then use erase tool to clip out intersection from the 2 other polygons separately. Then you will have 3 polygons. You can union them together if you want them in the same layer. I just noticed this post for qgis. If qgis has similar tools it might work. Good Luck!

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