I was in Scotland last month, using Apple maps with a rental car, and it was not reliable. I'd look up an address and when near the destination I would get instructions like "park the car here and continue on foot" to waypoints out in the wilderness, for the Helensburgh area. That's not a huge city but it displays correctly in Apple Maps and seems like it should work until you actually try it.

I reverted to the HERE maps app for navigation which worked perfectly, but does not appear to be compatible with CarPlay yet, so I had to use a mount for the phone.