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I am using 2.8.3-Wien to analyse two polygon layers, one with many more polygons (layer A) than the second. (layer B)

I need to know which of the polygons in A overlap with each of the polygons in B, as a new layer, with every overlap as a new polygon.

I've tried using Intersect, but I get a great big table with only half the data in it. It has all the polygons, labelled with data from B, but the fields which should say which polygon from A has overlapped is all null.

I had managed to get Intersect working with layers with less polygons, so is this just a processing power problem, or is there some other tool within QGIS that I can use?

I've not been using QGIS for long, so it's entirely possible I'm missing something really basic but vital.

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    Possible duplicate of Selecting features within polygon from another layer using QGIS? – Oto Kaláb May 10 '17 at 14:10
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    Not a duplicate, as either I'm using Intersect incorrectly, or it isn't working. – Poi May 10 '17 at 15:03
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    Sorry, you are right, I misunderstand it. I thought that you want select overlapping polygons (select by location), now I get it that you want create layer with overlaps (intersect). – Oto Kaláb May 11 '17 at 8:05
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I have diagnosed the problem. Shared field names!

Once I had created unique field names across both layers, the intersect worked perfectly.

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