Clive,

I like where you're going. When I tried your landclass file the building density immediately crashed my system if I tried to fly over a very large city like Paris or London. I have to use higher DIM values to get it to run. Even then I'm seeing some persistent stuttering if I'm at low altitude.

I tried reducing the tree texture file back to 2048x2048, and it helped some. (see attached)

a_largecitytrees01.zip