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I have polygon layers that I need to be covered by other polygon layers, and many of my inner layers have a vertex on the border of an outer layer or in some cases they share an edge. Both ST_Covers from Postgis and the topology checker ('must not overlap') inside Qgis confirm that some vertices are snapping outside of the outer polygons instead of on the boundary.

Is there any way to ensure that the inner polygons snap to the boundary instead of outside the outer polygons?

  • How did the polygons where created? Its a common problem when digitizing to have not the topology you want to have. That can be looked at when creating new geometries in the future. Or do you mean that the snapping tools are not working properly when you create the polygons? – Matte Apr 17 '16 at 20:31
  • I'm creating the polygons using the 'add feature' tool in QGIS. After looking at it more, it seems to be an issue when it's snapping vertex to edge, but not vertex to vertex. – user3747260 Apr 17 '16 at 20:44

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