# Calculating Areas in QGIS - Projection Scale Factor

I have a problem in calculating areas in QGIS. The data is in projection EPSG 25832 (ETRS89/UTM32). According to the cadastre, the feature has an area of 34025 m². If i measure the area of this feature with the measurement-tool it says 33920 m² (minus 105 m²). If i lable the feature with \$area it says 34034 m² (plus 8 m²). In our CAD-program GEOgraf we have a setting called 'Maßstabsreduktion', i think in english it could be the projection scale factor or scale distortion or scale reduction. We have the problem that we are at the edge of zone 32 to zone 33. So we have distortions in area and lenght. In GEOgraf we have to set this parameter to 0.9996 instead of 1.0000 and the program calculate a reduction in the area and in the lenght. If i disable this parameter in GEOgraf i get the same area, QGIS calculate for the label of this feature (34034 m²). If i enable this parameter in GEOgraf i get the area given by the cadastre.

So my question is: Is there a possibility to give QGIS such a parameter somewhere?

• One way is to créateur your own projection system to get better precision of your region of interest. – Hugo Roussaffa - GeoDatup Sep 27 '17 at 13:20
• Take a look at Project -> Project Properties -> General -> Measurements. You can choose between certain ellipsoides and none/planimetric. The cadastre may use that, while QGIS calculates more accurate on the bended ellipsoid surface. – AndreJ Sep 27 '17 at 18:22
• Ask from the cadastre authority how they have measured and recorded the area, and if the area is GIS area or manually saved area in the registry. Cadasters have very long history and stored areas do not necessarily correspond with computed areas. Landowner may have bought 20 hectares land 200 years ago and borders were marked into field with landmarks. If you now measure area by the landmarks you will not get 20000 square meters but that can still be the official area in cadastre. What is sure is that the native projection of the cadastre is not any UTM zone. – user30184 Sep 28 '17 at 6:05
• @AndreJ Thanks, now i know where to find this option... the correct ellipsoid is choosen. But i think the reason for the difference is the scale factor... with the use of the scale factor in GEOgraf the calculated area is the same as given by the cadastre. – Astrid Sep 28 '17 at 8:09
• @user30184 Thanks for your answer. I know, if you have an old parcel and you measure the area now, that you get another area than 200 years ago. This land parcel is rather new, partitioned 3 or 4 years ago with Tachymeter and GPS. So this shouldn't be the reason. – Astrid Sep 28 '17 at 8:17

• @Astrid if you run gdalsrsinfo EPSG:25832 in the OSGEO4W shell terminal, you see that the scale factor of 0.9996 is applied automatically. It hides in the ' +utm'. if you want 1.000, you need to build a custom tmerc projection instead. – AndreJ Sep 28 '17 at 9:37