See the above posts by Mr. Lovell who is also in the radio profession.
...and "Mr. Lovell" reminds me of how old I have become. "Bill" sounds better.
Getting back on topic: The Summit and Stark "MAC" talkgroups are nice because they are assigned by someone, and Geauga does the same with their 8 TACS, but actually, the same thing can be accomplished using the 15 "LECOMS" in all MARCS radios (except for the assignment coordination part) for everyone on MARCS. (...ECOMMS for State Incidents) The MARCS folks were very foward thinking when designing the template involving interoperability.