Bug report #14504

Updated by Alexander Bruy over 3 years ago

In a land cover study I want to derive country-wise land cover units in order to determine the area of each land cover type in each country. The source data is a land cover raster that I have vectorized and then clipped by a layer containing the national boundaries of the three countries in the study.

I then use Vector/Geoprocessing Tools/Intersect with the vectorized and clipped land cover layer and the national boundary layer as inputs. As I have made sure that both layers cover exactly the same area the result of the intersection should be land cover units divided by country whose total area should be the same as the total area of all land cover units prior to the intersection.

It turns out that this is only the case for a few land cover types. For most of them the total area after the intersection is significantly lower than the original area, indicating that the intersection operation does not yield complete results. As an example the total shrubland area is reduced with about 35 % in the intersection operation.

In order to provide a possibility to reproduce the problem I attach an archive containing the national boundary layer and an extract from the land cover layer containing shrublands only.

I have tested the analysis using both QGIS 2.8.7 and 2.12.3 and the problem is the same in both versions. I am running QGIS using Windows 8.

When checking already submitted bug reports it appears that #13246 may be related.