Hah, thank you!
The dome is actually just a solid sphere brush chopped in half. I am really struggling with creating hollow domes at the moment. I'm quite confident with bevels, cylinders and arches but it's where to put them is what I'm having the issue with. I get to a point where I just sit and stare at the map until I think to add something to 'flesh it out' a bit more.
As for the mountains, I believe they are vjun cliffs. I tried hoth mountains_a and mountains_b but for some reason they weren't rendering properly.