My iPad has cellular service built it, but to ensure that can reach some sort of cell service, I have the Weboot Reach device. It is a cell phone booster. Came with a small magnet antenna that I mounted on roof and ran into the cab. The cell phone booster has one end of the amplifier cord/antenna next to my cell phone so I can always get the strongest signal to that device. Then I can run whatever GPS map app such as GAIA, Apple Maps, Google Maps, Waze, etc. and mirror to my Apple Car Play screen.
If I didn't have the Apple Car Play screen, then I would just look at map on my iPad, which I have an iPad seat post mount/goose neck. I have my Ham Radio on top of my dash cause I just don't have any other real estate on my rig.