Okay this is copied from some very old SA posts (sorry don't know who posted them originally) and modified for JNFWoP, but it might prove a starting point for some other ideas...

                                                                            ^
                                                                            M
                                                                           MM
                                                                         MMMM
                                       ddd #              ss  #  uuuuuuuMMMMM
                               mmmmmdddddd # ss          ssss # uuuuuuuuMMMMM
                           llllmmmmmmmmdddd#ssss       sssssss#uuuuuuuuuuMMMM
     ???#      #        11llllllllmmmmmmmdd#ssssssssssssssssss#uuuuuuuuuuuMMM
   ?????#C  CCC#       1lllllllllllllllllll#####s###s########################
  ??????#CCCCCC#lll  llllllllllllllllllllllllllssssssslllllllllllllll#???????
  ??????#CCCCCC#lllllllllllllllll-----------llllllllll--------------####?????
  ------#CCCCCCCCCCCCCCCCCCCCCCC-           ----------              ---###???
        ------------------------                                       --####
                                                                         ----

(Hope the page width doesn't screw this up. If it does copy it to a text editor and line the perimter walls up, everything else should fit into place)

Where:
C   :   Cannibal sectors.
d   :   Upper Downtown.
m  :   Mid DownTown
l   :   Lower DownTown. (1)
s   :   Suburbia.
u   :   Uptown.
M   :   Mort Central.
^   :   Slayers office.
#   :   Walls.
?   :   Unknown, possibly reservoirs or redundant industrial facilities
-  :   lowest recorded depths

Scale:

each letter to dt perimeter is width 10km afterwards width is 100km per letter.

depth is 20 storeys per letter

It is a generic cross section from Mort central (rhs) through CS1 (lhs)

The Perimeter walls that are underneath in JNFWoP aren't manned, just imagine 100ft of reinforced concrete as foundations. There are a few known gaps in this base area, for example in Suburbia (which Carrien and Serial Killers can utilise to try getting into Uptown.)

Mort Central:

50 miles square in the MRB, IIRC

Uptown extends from 50 miles to 150 miles radius from Mort Central, Suburbia 150 to 350 miles, DownTown out to about 2500 miles. In JNFWoP each squad tends to be based in a specific area for an extended time period because of the vast distances required otherwise. Gauss Trains travel at 500 miles/hour, so to get to the furthest distances of DT it would take 5 hours of Gauss travel. Or fold-miles from Dark Lament...