You right Nick, I took Landclass away and this is the result in default (full slide autogen & scenery complex)

I hope SP1 fix for not to use Landclass
Cheers
If your mountains and area look OK without the landclass leave it disabled. If the mountains, hills, flat land and forest area are not where they belong then unfortunately the landclass is the only way to put the topography and land in the correct order.
There is a scenery editing software by Abacus that makes it easy to add scenery but I do not think you can remove what is already there. I am not sure about that though Alrot. What really needs to happen is someone needs to make entire area of Valencia in a complete build, otherwise you are at the mercy of what the default and generic add-ons put in the area.
As the other thread where you and Miltest were discussing the problem shows, even with the best mesh available Lake Valencia is on a 100ft plateau. That is not the fault of the mesh or the landclass but Microsoft for not getting the lake and land elevation correct to begin with. That is why your airport was in a hole. The airport elevation was somewhat right, and everything else in the area was wrong. Hopefully they will have fixed that in SP1. I do not have a copy here in front of me to fly so I can not tell you that it is or not. Its currently in B2 status and will probably hit the servers at the beginning of next month at the latest if everything checks out this time around.