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I have a geopackage layer in QGIS which contains block outlines for parcels of land. They have been digitised with a gap between each block but the edges of adjacent polygons should actually share an edge. I'm looking for a way to calculate the midpoints of the gaps so I can drag the edges of the polygons to this point. Searching online I found that ArcGIS appears to have a tool that would help do this - midpoint, but I can't find a similar feature in QGIS. Can anyone suggest a method I could use?

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  • Is that one multipolygon with three parts or three polygons? Can you add another screenshot showing some more examples?
    – Bera
    Commented Aug 30, 2022 at 6:02
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    Those are three separate polygons. Each block is a separate polygon apart from a few exceptions which are multipolygons but these tend not to be closely adjacent.
    – CCJ
    Commented Aug 30, 2022 at 6:21
  • You could extract vertices, then join attributes of the closest vertice within say 10 m, change your point geometries using the field calculator by calculating the middle between the point and the one you joined the attributes from, and finally convert your points to lines and those to polygons. But this process falls short for three adjacent polygons. Maybe it gives you a direction.
    – Erik
    Commented Aug 30, 2022 at 8:22

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Centroids processing tool.

However this will require a bit of prep. My recommendation is that you convert your polygons into points using the 'Extract Vertices' tool. This will give your the corners of each poly. Then select the two opposing corners and use a Point-Line tool (eg: Points to Path).

Do this for each opposing vertex.

Then you can use the 'Centroids' tool. This will create a new centroid between the two, which represents the midpoint.

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  • As you currently describe your workflow, it will return the centroid of each selected vertice, aka the vertice itself.
    – Erik
    Commented Aug 30, 2022 at 7:41
  • lol my bad. i totally left out half the answer, let me fix it.
    – nr_aus
    Commented Aug 30, 2022 at 8:36

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