Ok, from how I understand it the system is split into two zones. North Zone and South Zone.
North Zone is a set of simulcast TX/RX sites poss around 6, and South Zone the same.
There are then a number (i've got two from all the previous submissions to the DB) of fill in sites which are independent from the two simulcasts. These fill in gaps where simulcasting the frequencies wouldn't be viable or effective due to the layout of the system. The system also has multiple remote receivers and in-building amplifiers to provide good indoor talk-in coverage into the system for portables.
Alltogether there are 24 sites in the system, with a mix of TX/RX, RX only and Microwave link only.
From looking at the old Police TG allocations, most operations were split into North/South and those TG's would be locked into either zone.
This was done so the radios only tie up a frequency on their respective simulcast. If they set the radios to roam the entire system, if one officer who was on the North simulcast TG 'North 1' for eg. went into the service area of the South simulcast, the system would have to allocate a frequency and that would tie it up for other users.
I expect full roaming was restricted to Countywide channels to preserve frequency resources, allthough the system seems to be so powerfull anyway that I imagine either zone would be useable in most of the county.
Phew my keyboard is on fire now......