When I retrace a polygon using the measure area tool and get what I believe to be an accurate area measurement. However if I utilise the field calculator within the attribute table to calculate the area of all my polygons, I get a significantly different area measurement than the one above which I believe to be completely inaccurate.

What is the cause of this discrepancy?

Any ideas why the field calculator is throwing out the wrong figures ? I'm using a WGS84 projection - EPSG4326

  • What formula are you using to calculate the area? – ndawson Jul 8 '20 at 18:46

I'm using [...] EPSG4326

there's your problem. This CRS is based on degree, so any distance/area calculations you do on this layer are done in degree, too.

Save your layer to a CRS based on meters, which fits your area of interest, then do the calculations.

  • Thanks Erik - Does OSGB1936 EPSG 4277 seems a sensible alternative ? – catfordbags Jul 8 '20 at 11:23
  • I have no idea, if it fits your AOI. – Erik Jul 8 '20 at 11:24

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