Topology in QGIS shapefile, GRASS and v.clean (nested polygons)

Question

Following this: Nested polygons in QGIS overlap and don't show the real colour gradient

I applied the GRASS function v.clean -> break as suggested by @ahmadhanb and the shapefile now shows correctly all the nested basins without using the Feature blending mode = Multiply.

However I noticed that in the attribute table the v.clean function created ~2 times more variables than the original shapefile (e.g. original shapefile 250 polygons, after v.clean 500 polygons). There are then duplicated polygons that eventually create issues when doing a Join.

How can I remove the duplicated polygons created by v.clean and keep ONLY the 'good' ones that appear in the QGIS environment when selected?

I tried to apply rmdupl within v.clean but the shapefile did not change at all!

Answer 1

Another possible solution instead of rmdupl within v.clean is to use Delete duplicate geometries from QGIS Toolbox -> QGIS geoalgorithms -> Vector general tools -> Delete duplicate geometries.

I tested on the following polygon shapefile that has duplicate polygons:

I used Delete duplicate geometries tool

The result is a shapefile without duplicate polygons.