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After I merge/dissolve polygons together, the area I calculated using the field calculator seems to decrease, in comparison to the calculation of each individual area and then summing it up. Can somebody tell me why this is happening? I am using the same projection (Europe equal distant EPSG: 102031) and the same method $area in the field calculator.

closed as off-topic by Vince, Ian Turton Aug 13 at 16:11

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "This problem cannot or can no longer be reproduced. Changes to the system or to the asker's circumstances may have rendered the question obsolete, or the question does not include a procedure to enable potential answerers to reproduce the same symptoms. Such questions are off-topic as they are unlikely to help future readers, but editing them to include more details can lead to re-opening." – Vince, Ian Turton
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    Hi Rahma, do some of your polygons overlap? – ian Aug 13 at 11:02
  • What GIS software are you using? – PolyGeo Aug 13 at 11:20
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    Hi ! Thank you very much !! Yes, you were right I had overlapping polygones – Rahma Aug 13 at 11:21
  • I am using QGis. – Rahma Aug 13 at 11:23