How to clip a single layer of overlapping polygons in QGIS

Question

I have a single layer of polygons. Some of the polygons overlap.

I wish to make a new layer of just the parts of the polygons that overlap.

What is the best way to do this in QGIS seeing it's all in one layer?

I tried the clip and intersect in the geo-processing tools, but they expect two layers.

Answer 1

There's is a rough and dirty way to do it. I say rough and dirty because I've been getting strange intersect results which I'll open a bug for.

1. Use Vector > Geoprocessing Tools > Intersect... with the layer as both the inputs.
2. Use the Spatial Query () tool and select features from the intersect tools output that "Equal" your source layer.
3. Start and editing session to remove those selected features in your intersect results layer.

Depending on the complexity or count of the features, running these can take a couple mins.

Some optional additional steps could be if you have an ID type of field with common or unique attributes do a dissolve then a Singleparts to Multipart.