If using a GPS, then when setting up the programming file, be sure that you also import or enter the location information for each department, and/or tower site for trunked systems. Otherwise, if location is blank, it would never be enabled. But at least, if you have all the location data included in your programming, then the GPS would keep the scanner focused on what is in range.
If you were to just program the entire route, it would slow down scanning so much that you would miss a lot of conversations. You could reduce the wasted time by breaking the trip into sections, like each day's, or half of the day's, itinerary, then control what is active by using Startup Keys. You start the scanner, while holding down the 1 key, and any systems set to that would be the only ones enabled. When you reach the end of that section, press and hold down the 2 key while the scanner is powering up. Again, only the systems that have that startup setting would be scanned.
The 325P2 has "25,000" channels of memory. but some items may use more than one of the 'channels'. As long as you stayed, mostly, with the state agencies (state troopers or highway patrol), plus dispatch frequencies or talkgroups for each county sheriff's office, as well as medium to large city PD dispatch, along with fire/EMS dispatch (for accidents along the way), I suspect you just might be able to cover the more significant happenings along the way. But if you tried to program everything, in each county, you'd exceed the storage limits. This is where the database scanners from Uniden have the advantage. Using an HP series scanner (HP-1/-2, x36HP or SDS), you always have the full database available, and you can let the GPS handle what is enabled and what is not. If you'd rather fine tune what's selected, you can use append to pull the systems from the main database, including location data, then select hat interests you, customize text tags, or anything else, and still let the datbase handle the nuts and bolts of what is active and what is not.