Thanks for the feedback guys!
Yeah, textures are not up to date but I made them pretty consistent throuout the map so it might be a style question.
I have put down some information on how to build such a map if anyone is interrested.
First I started laying out my map with a 16 bit heightmap texture which I then transformed into displacement patches using DispGen .
Next I worked on them in hammer for my desired look, small/big changes here and there until the map finally reached a state like this in the overview (note the square patches which form the displacement surfaces):
Now one thing is a bit tricky to figure out and you might need it for building holes. If you want a hole in your map, select the patch where the hole should be in and cut from the 4 corners to the desired hole you want in your map ( Out of one patch you make 4 and a hole) - Looks like this:
Have fun!