1

I noticed Polygon shapefiles that were edited with ArcMap yield many errors in the QGIS Topology checker.

The picture below shows a polygon Shapefile. I made one error on purpose so the topology checker shows there is just one error (checking for overlap within the layer)

enter image description here

Next I edit this layer in ArcMap, creating a hole between two of the polygons

enter image description here

Then I use the QGIS topology checker again, yielding 3 additional errors.

enter image description here

Now my questions are:

  • Can I change some settings in ArcMap so that it will not create this difference? I think it might be saving the vertices of the edited polygon with a lower precision.
  • if it is not possible to fix it in ArcMap, then what is the quickest method to clean these tiny errors quickly afterwards with either QGIS or PostGIS?
|improve this question
  • 1
    To fix the error in QGIS, try the processing tool snap geometries to layer and snap the layer to itself, with a very small tolerance. You probably don't want the default behavior ("prefer aligning nodes, insert new vertices where required"), but rather "snap to anchor nodes" or "prefer aligning nodes, don't insert new vertices". – csk Jun 4 at 20:09
  • Are you using a map topology to edit in ArcMap? When you split a polygon you are adding a vertice at each end of the cut line to the polygon you are cutting, but not the adjacent polygons, thus creating slight gaps or overlaps. Topological editing would supposedly add a vertex to the adjacent polygons in the same location. – johns Jun 4 at 20:30
  • ArcMap requires you to explicitly create a topology if you want it to maintain a topology. It won't automatically derive a topology from a shapefile. In fact, I think that ArcMap may require a geodatabase to do topology and won't do them with Shapefiles at all. ArcMap also requires the 'Standard' or 'Advanced' license to manage topologies. It won't do it with a 'Basic' license. – Son of a Beach Jun 5 at 3:13
0

The method suggested in the comments by csk works for cleaning the geometries

I created the errors in the below image using ArcMap 10.6 by simply moving vertices and placing them back on their original location. In QGIS the topology checker reports these overlaps.

enter image description here

Using snap geometries to layer from the processing toolbox resulted in a shapefile without overlap or gaps. See below screenshot for the settings (I think the English name for the mode will be snap to anchor nodes as suggested by csk)

enter image description here

|improve this answer

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.