[GIS] Identifying number of overlapping polygons in QGIS

Question

I'm looking for a possibility to identify the intersecting parts in one single polygon layer with ten features, where at least four polygons overlap. How can I do it in QGIS?

Answer 1

I would use Join Attributes By Location, located in the Vector menu, under the category Data Management Tools.

Choose the option Take Summary Of Intersection Features, and check the box sum. This summarises all numerical attributes of the intersected polygons in new attributes (which you didn't ask for), but it also creates an attribute called Count, which lists how many features touched each intersected feature.

I just tested this with two polygon layers, and it worked fine.