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I am learning on the job with QGIS.

I have two state level vector layers with individual shapes for each county inside the state boundary. I am trying to identify the area differences between each county within the state layer between the two files. I've tried the following using shapefile and geojson format: I processed using the difference tool but this only gives me the difference between the state boundaries, rather than the difference between the overlapping counties inside the state boundary.

I would like the symmetrical difference between each of the counties, but this tool also only gives the difference around the external state boundary. The only unique field in common between the two layers would be the name, but there are some different spellings. There is the 'Split vector layer'under data management tools, but I would want to scale this up.

How can I get the polygon area differences between the individual counties?


@LuisPerez Thanks for the response, below is two images. The data is admin data from OSM, compared to another layer from the government. In the zoomed in image you can see the spatial differences, and my idea was to perform 2 differences from the vector-geoprocessing tools options, reversing the role of input/overlay in the process. I would then look at differing areas between corresponding features between both datasets Zoomed out admins

Zoomed_in_yellow_box

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    could you please provide some example datasets ? – the_darkside Oct 23 at 18:48
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    Could you place some images that better describe your case? – Luis Perez Oct 23 at 20:44
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Try Union then symbolize using rules or select/extract by expression etc:

enter image description here

| improve this answer | |
  • The union process fails when attempted. Ive tried smaller numbers of features, and also reinstalled QGIS just in case. It is the same with the Difference geoprocessing option under the Vector menu – oisin78 Oct 26 at 18:18
  • With what error message? – BERA Oct 26 at 18:49

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