Treasure Island (T.I) is part of the Southern Police District.
There's ten policing districts in S.F., each labeled with a letter. The oldest is Co. A, Central (i.e. Chinatown, Downtown, North beach areas) and the newest is Co. J, which encompasses the Tenderloin District.
The trunked radio system is a bit of a mess (in coverage, usage, feedback problems), as there are two channels assigned to each Dispatch Area. The Dispatch channel is used in the radio cars (taking the place of the old Low-Band 45MHZ system, and these are still in the cars as a back-up system). The "Service" channel is for the hand-helds, replacing the old UHF P.I.C system.