This is in my opinion one of the biggest shortcomings in the software (both DJI Go and Litchi apps). There should absolutely be an option to save offline maps indefinitely. Caching is completely flawed. Not only do you have to do this awkward dance of zooming into an area and manually moving the screen around... but I've had numerous instances where I did this, didn't close the app down, and still came up with a blank map screen when I went to fly. To be honest it's not a huge problem if you aren't moving much from the Home point because GPS will be able to show you where both the Aircraft and Home are (you don't need data service for that). And if you have GPS on your smart device, it should show where You are too in real time. So when you are ready to back home, point the arrow towards home and fly forward to it. Same goes for RTH, it knows where you are. The map might be blank but you don't really need it for getting it back home.
There are two scenarios however (that I can think of) where not having a map is a problem (both only applicable if your device isn't reporting your RC's real time location).
1) if the Mavic crashes or malfunctions and goes down, it'll record the last known location. If you don't have your real time location showing in the app then you have to refer to landmarks and features on the map to orient yourself and refine the search location. But..... if you don't have a map, that's going to make things REAL difficult.
2) if you are on the move, say a boat or a car, and you don't have a map or real time RC position, it may or may not be difficult to locate yourself based off the camera's view alone.
I experienced the second scenario in Costa Rica while being driven in a car while I piloted. I couldn't find the car from the air as the landscape was all very nondescript. So I kept calm and drove back towards the home point and rendezvoused with the Mavic there.
My biggest piece of advice to anyone who will be subjecting themselves to scenario 2 is to use a device that has GPS and double check to make sure that you can see your real time position on the map, along with Home and Aircraft.
The iPhone 7 (at least the 7 Plus but almost certainly both) has a compatibility issue with the DJI Go 4 app where it will not show the phone's position. But it does work and show up in the Litchi app so (come on DJI, really?!?). I learned that the long hard way after hours of troubleshooting and finally breaking down and getting on a lengthy chat with tech support. It took me a while to get the answer out of them despite painting them a crystal clear picture of the conditions. I chewed them out a little bit and he said he'd escalate the issue to the development team so hopefully there'll be a fix soon.
Good luck out there!
