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I made a QGIS project to calculate some measures about the city I live in (in Belgium). Problem is, I noticed that I get very different results when measuring elements, in Google Maps vs in QGIS. Example: the same line measures 2.5km in Google Maps while it is 3.2km in QGIS.

I guess this is related to a wrong CRS - I didn't change anything when I created the project, those are the default values. Mine is EPSG:3857 for the project. It seems that there are also per-layer CRS, but they are also ESPG:3857 (WGS 84 / Pseudo-Mercator).

How could I fix my project so that I can measure the correct distances? Will it fix the existing layers and measures?

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    Do not use EPSG:3857 for any measurements, it is way off real values. Use a local projection for your area of interest. See gis.stackexchange.com/questions/396004/…
    – MrXsquared
    Feb 1 at 8:31
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    Also remember to set "Measure" tool if it is what you are using to 'Ellipsoidal' and not 'Cartesian' if the crs has an ellipsoid (which is the case for EPSG:3857) will at least allow you to have measures close to accurate
    – Louis Cottereau
    Feb 1 at 8:37
  • Ok, how could I choose the correct CRS, and will changing the CRS in the project parameters fix my issue ?
    – gordie
    Feb 1 at 8:55
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    @gordie The crs EPSG:31370 is based on the offcial datum (BD72) for belgium.
    – Louis Cottereau
    Feb 1 at 9:52
  • Hum nevermind it was the official one 22 years ago not sure now EPSG:3812 might be it
    – Louis Cottereau
    Feb 1 at 10:17

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