7th pct usually uses the LIE as the dividing line as to whether to use North or South. Generally speaking.North and South are "switch downs" so units can talk without having to tie up the respective dispatch talkgroup. Pcts 1, 3, 5 use South and 2, 4, 6 switch north. I'm not sure about the 7th. Other commands like ES, Hwy and K-9 will just specify what to switch to. Usually the LIE is the dividing line between the two.
North and South are through the system, so it can be heard countywide. Car to Car is not repeated, its simplex so its range is limited, usually a mile or less on mobiles and even shorter on portables.