3 and 4 are above ground. (Same place, just divided by the Citadel.)
5 is the labor zone. This is where most work in the Citadel takes place.
6 and 7 are filled with the rich! They are guarded and have better service than those above.
Pretty much everything else is underground!
8 is a general cave region, which is most of the world.
9 is the refuge/starting area, where your adventure begins!
12-15 are the lush caves.... They've been overgrown with plants, and travelers don't often venture down there...
(13 and 14 are the same zone, just divided -- like 3 and 4)