I am running topology check "layer should have no gaps" and the result shows one error with feature id 0. Double clicking on the error shows a large Dodecagon that is not part of my layer. How can I further troubleshoot and identify the gap?

1 Answer 1


If you could upload a picture, that would help with any answers.

However perhaps try the following?

  1. The dodecagon might be the "gap", i.e. the view in red. If you uncross show errors on topology checker, you might see the "gap" inbetween the polygons/features on your layer. View of a gap

  2. If you use the select tool, you could delete the surrounding polygons to see if the Dodecagon with vertex (crosses) is visible. If so, I think this might then be a "ring", so if you undo your changes, you could use the Delete Ring button to delete it.

Delete Ring

I would suggest taking care not to save the deletions to the layer, or you could save a copy of the layer to test this first.

  1. Or if you open the attribute table for the layer, you could potentially identify which feature is the problem, by selecting the numbers on the left hand side of the table. Each number corresponds to a feature on the map, which if you select a number, (for a polygon style layer depending on style settings) the feature is highlighted in a colour, I think the default is yellow. This would allow you to confirm that yes, it isn't a feature on your layer, as for example, it could be a multi part polygon.

If you press zoom map to the selected rows, this should zoom to feature selected in the attribute table.

Zoom to a feature

  1. Try zooming at small scales to see if you can see "overlapping" lines at the edges of the Dodecagon. If there is an overlap, try snapping the lines to one shared common line.

  2. Or try to identify if the Dodecagon has vertex (crosses) by trying to select it with the node tool. Sometimes I have needed to add extra points by double clicking for the "feature" to be visible enough to select it and delete it.

    ^^ In my experience, I find some gaps/overlaps are still visible in the topology checker, which I assume are tiny, as I can't see them when zooming in a small scales.

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