the airport in FS is placed on a plateau, which is`t corresponding with the real thing. I`m using FS Global ... might this be the point ? and is there a solution, to get the surroundings as flat as they should be ?
That's an usual problem if you use addon meshes, which sometimes don't have the correct height. The airport is obviously placed at its real world elevation, which is 1411 feets, but there are two issue at play here:
1) The mesh might not have the correct altitude close to the airport. This can be checked if the plateau is all the same height difference with the rest of the ground
2) Flight sim doesn't support sloped airports and at Geneva this is an issue, because the airport is at 1411 ft, and the runways are at 1407 and 1365 ft on the two ends. If this is the case, the plateau would look not all the same along the aerea.
There's nothing we can do to fix the scenery, we can't obviously change its height to a non-real world value to match a specific mesh, because it might not match another one or the default scenery.
And, it would not be 100% fixed anyway, because the runway ends have different height so, you will always get some kind of elevation problem at one end.