[N7YUO]

Compare if you will, the Davis radios (or any others) to a cell phone.
As I travel down the road, my phone seeks out a cell site with a strong data channel.
If the signal level drops because of distance, terrain, or structures, the phone will seek
another site.

UCAN radios work with a similar principle. They seek a strong site. If the strength of the data signal drops, they seek another strong site. That site could be in the next county.

Some Talk Groups (TGRPs) are authorized to use all sites. (Life Flight, AirMed).
Some TGRPs may be restricted to using only their local sites (Street Department)
When the cop from Sunset drives his patrol car to Wendover where he moonlights as a security guard at a casino, the Wendover site may transmit Davis calls if he left his radio on.

Some undercover teams get creative to avoid their comms being intercepted.
I once heard surveillance in Layton (Gentile Street), they were on (SL Simul) using the
Tooele event TGRP.