OK for the newbies: Some Wide Area Trunking 101-
Any radio that affiliates with the site your monitoring will allow you to hear ALL Talk Groups that are programmed into that radio's code plug. For example, an ISP high ranking officer happens to get assigned, or goes for some reason to an area near the site your listening to. As long as his radio is affiliated to that site, you will hear traffic on any of the TG's in his radio when there is activity on them. Lets say his home area is D-52, but he is assigned to D-14 for some reason. He switches his radio to the D-14 TG's to talk with Dispatch, and the troopers, as well as operate on any of the OPS TG's. His radio still has the D-52 TG's in it, and now you can hear those as long as he is on that site.