I am trying to identify the overlapping lines within a layer that consists of polygons of land parcels.

I have already converted my data to lines and exploded those lines. Indeed, I have run a "no duplicates" rule with the Topology checker and it identifies the overlapping lines (shown as red in the image below). But I do not know how to select the data identified by the Topology Checker.

When I run "intersect" on the layer, it seems to return all my data, including the non-overlapping portions. Is there any built-in tool that can help me here? If not, I assume this would be a straightforward SQL query?


  • Try running 'remove duplicate geometries' from processing toolbar
    – MrXsquared
    Jun 5, 2019 at 19:25

1 Answer 1


I honestly don't know how to extract overlapping lines through the Topology checker. Let me suggest another tool - SAGA: Shared polygon edges, which is available in the Processing Toolbox.

enter image description here

  1. Activate Shared polygon edges tool from Processing Toolbox > SAGA > Vector polygon tools.
  2. Select a unique id field in your polygon data (e.g. "fid" in this example).
  3. Give a small Tolerance to ensure the tool recognizes all overlapping edges... you may have to give a trial and error... 1.0 meter worked for me in this case.
  4. Tick on Check vertices
  5. Run the tool.

You will then obtain a line layer Edges, which would look like below:

enter image description here

  • I have changed the Edge layer style to green dashed line.
  • Open the attribute table to examine which edge has come from which polygon(s).
  • If you select any of the edge, corresponding attribute record will show id (ID_A and ID_A) from the original polygons to which the edge belonged.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

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