Originally Posted by
Steve B.
If the app uses a map that is not a resident file on the phone, then cell service is required to visualize and display the map and route. You see this often with Google maps if you are in an area of no cell service and neglected to cache a map set local to the device.
For a "long trip", if you are using "a map that is not a resident file on the phone", then "you are doing it wrong".
People using phones for navigation should have resident maps on the phone (as a backup if they prefer using something that isn't resident).