Duty posts were mentioned earlier, but kind of glossed over, so I'll add a little insight to that.
Let's take an area near me:
Division 1 - Richmond (has 22 counties and four cities in it, and includes Areas 1, 2, 3, 4, 6, 7, 8, and 44)
Area 6 - Chesterfield (has three counties in it - Chesterfield, Powhatan, and Amelia, each of those counties is a Duty Post)
So a trooper would be assigned to Division 1, Area 6, Duty Post 2 - meaning his/her primary area of responsibility is Powhatan County. However, that doesn't keep them from being assigned to patrol and handle calls in Duty Post 3 (Amelia) for the day, or on midnight shift they might be patrolling both Duty Posts 2 & 3.
As Nitsud said, the wrecker zones are relative to the Area Office. So going back to the above example, you could have Zone 6-1 through 6-7 for Area 6: 6-1 through 6-5 would cover different areas or roads within the Chetserfield County which is very large and populated, whereas the more rural counties would just have a single zone to cover each county (6-6 for Powhatan and 6-7 for Amelia).
Please note I simply made up those Zone numbers for Area 6, it's been 15 years since I had to have that one memorized.