No, you have full control over the terrain, and the editing tools are pretty good. You do need to use them too, as the challenge and sandbox modes start off with completely flat terrain which needs some sculpting to look interesting. Coasters and flat rides can be set to automatically tunnel through terrain if needed.
I think I'm done with my sci-fi area, though I may come back and replace rides with others later on as I research them.
The G Force Extruder (I wanted to give all of my rides silly names)
And Re-Entry, my first fully original coaster with full station building. I'm quite proud of this: