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In QGIS 3.22.0 (Biatowieza) by means of the "OpenRouteService" Plugin I was able to get isochrones for my point layer.

The "ORS Tools" Plugin calculates the population within the isochrones. However, I have overlapping polygons, and when I intersect them, I cannot deduce how many people are all of my polygons. Most of the people are counted double or even triple. Can somebody explain why does it happen?

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If I understand correctly, you want to know how many people live within a given time-based distance from your points. For instance, how many people live within 5min of a mailbox. Based on the ORS Tools documentation, the isochrone and population within is calculated for each point. As a consequence, if isochrones overlap, the people living in the overlapping area are counted twice or more when you sum them up. That is for the "why".

The documentation also states that the population calculation is based on a GHSL dataset. If you want to work around the issue, then maybe you can merge the isochrones, download the dataset and make the calculation yourself.

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  • Thanks for this approach. It does sound like a good workaround. However, I'm a little confused as to which dataset I should download from GHSL in order to do the calculation. I looked at the list of data, but wasnt quite sure how to go about it.
    – rtaani
    Commented Nov 9, 2022 at 16:26
  • I am not familiar with GHSL. And the ORS Tools documentation does not provide further details. I think GHS-POP is the one.
    – ChloeG
    Commented Nov 9, 2022 at 17:16

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