The rules of surrounding terrain

[The_Turkish_Moose]

I couldn't find a guide about the surrounding terrain. I already know that no overgrowth or undergrowth can be used but I wanted to know what I can put into the surrounding terrain

[Mineral]

there aren't really any rules about it I think. It's just advisable to place much there, as the only function it will have will be to be a visual thing to look at. Unless if you make it playable area ofcourse which is also not really a good idea.

I would say place as less as possible, but try to make it not look too artificial going from normal terrain to surrounding. Meaning if your city stops, place a few buildings there too(like ramiel), or don't make a forrest abruptly stop,place a few static trees,... (like ia drang)

[The_Turkish_Moose]

Ofcourse, I wasn't intended to design entire cities in the unplayable area and I was only planning to add a few trees and buildings

[Mineral]

yeah that should be fine in my experience. And should make it look better

[Rhino]

You can't put trees into the the surrounding terrain, but you can put the tree lods in there.