[QGIS-Developer] Difference in area calculation using memory vs output layer

[Nyall Dawson]

On Wed, 8 Aug 2018 at 18:06, Rudi von Staden <rudivs at gmail.com> wrote:

>
> I did also calculate a range of zonal stats on the layer (which has only one multipolygon feature), but those results were consistent between output / memory layers.
>
> Is the area difference expected because of how shapefiles store geometry vs how they are handled by memory layers, or could there be a bug somewhere? Maybe this isn't the recommended way to calculate area? In case it matters, I'm using a custom CRS:
>
> "+proj=aea +lat_1=-24 +lat_2=-32 +lat_0=0 +lon_0=24 +x_0=0 +y_0=0 +datum=WGS84 +units=m +no_defs"

This may be a silly question -- but can you confirm that both layers
are definitely in the same CRS?

If so, I'd try exporting the two geometries to WKT and inspect for
differences. I can't think of any other reason for the area to be
different! (Since you're directly calculating the euclidean area
ellipsoid settings won't come into play, which is the most common
source of "different area calculations").

Nyall