The line between North and Central goes something like this (although not exact):
From West to East, just south of 78, then follows Route 287 southeastward to route 440.
2 Comm units cover Sussex County
3 Comm units cover Warren County
4 Comm units cover the Route 80/280 corridor (and 287 North or Morristown)
5 Comm units cover the Route 78/287/24/440 corridor
Hope this helps.