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I am using QGIS 3.4.1 on Windows 10. Project CRS is EPSG:3857 (WGS 84/Pseudo-Mercator).

I have defined a vector grid. Type is Rectangle (polygon). Horizontal and vertical distance is 50 m. Overlay is 0 m. GRID CRS is EPSG:3857. This goes well. But after selecting one of the polygons, the Cartesian properties are quite different from the Ellipsoid properties: - Cartesian: Outline: 200 m, Area 2500 m2 - Ellipsoid: Outline: 122,536, Area 938,435 m2 - Using the measurement tool shows sides of the rectangle of 30,567 m.

I expected a small difference between Cartesian and Ellipsoid outcomes, but this is impossible.

Does anybody have a clue of what is going wrong?

  • where about are you testing, try nearer the equator for a better answer – Ian Turton Nov 20 '18 at 14:01
  • My application area is The Netherlands – Henk Schaap Nov 20 '18 at 14:05
  • 3
    too far North for Pseudo-Mercator to be anything like correct. – Ian Turton Nov 20 '18 at 14:05
  • The scale factor increases in a Mercator projection as you move away from the Equator. At 52° latitude it is approximately equal to sec(52°) = 1.62 meaning that your distances in epsg 3857 will be around 1.62 times greater than reality. I suggest you use a map projection better suited for your area of interest, that would minimize distortions and give you better results if you wish to do 2D math on your map. – FSimardGIS Nov 20 '18 at 15:50
  • For the Netherlands, try one of the Amersfoort based projections, or ETRS89 / UTM zone 31N – AndreJ Nov 20 '18 at 16:05

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