The area of the polygons in a layer, calculated by the field calculator with "$area" is wrong (much too big) for some polygons. If I draw the concerned polygon again, the area is calculated correctly. It looks like the polygons really have a wrong size, but the centroids are calculated correctly.
edit: Thanks for your replies so far. Here is an example with some polygons. For some, the area is calculated right, for some not (as I said much too big). For example the polygon with the ID 669. If I redraw it, the area is calculated right. The problem is, I have >1400 polygons, and I don't have the time to check and redraw every single one.
Maybe someone got an explanation/solution?
Best Answer
@DarrenCope made a very good point, your layer contained inconsistencies.
Please note: I only posted this as an answer as to include a screenshot of the results, please accept Darren's answer when he posts one as he came up with the correct solution.
I used the Multiparts to singleparts function (via Vector > Geometry Tools > Multiparts to singleparts) and then re-calculated the area in a new column with Real numbers and precision of 2:
Ironically, enabling the "on-the-fly" option for CRS gave the correct results as it often provides wrong values. The CRS I used was:
EPSG:4326 - WGS 84.