English user manual stays at page 34:
- Mobile cellular data is required to use  DJI Fly...
- Cash the map data of the area where you intend to fly...

So questions to the community please:

1. Is it correct to assume that WIFI shall be off when using DJI Fly to minize interference with controller link to aircraft?
2. Will app work and will Mavic Mini fly of my mobile is out of the carrier network coverage? There were quite few such places say at Iceland?
3. How to cash  maps please?

From DJI in another similar post:   Hi, thank you for posting your inquiry for the DJI Mavic Mini. For the cellular data indicated on the page 34 of the DJI Mavic Mini manual, you can use data or wifi for updating and logging in to your DJI account. Once all needed updates are complete and you are logged to your DJI account on your DJI Fly application, you can fly the drone without using your cellular or Wifi services. If you have further queries feel free to DJI Forum. Thank you.

J-dub Posted at 2019-12-5 08:09
From DJI in another similar post:   Hi, thank you for posting your inquiry for the DJI Mavic Mini. For the cellular data indicated on the page 34 of the DJI Mavic Mini manual, you can use data or wifi for updating and logging in to your DJI account. Once all needed updates are complete and you are logged to your DJI account on your DJI Fly application, you can fly the drone without using your cellular or Wifi services. If you have further queries feel free to DJI Forum. Thank you.

Thank you. Waiting for my min and a refurb iPad mini with only wifi to arrive and hoping I didn't make an error with the ipad.

Turn on airplane mode (no wifi, bluetooth, cellular data..) once the drone is ready to fly, maps loaded, satellites ready etc. That way you have maps loaded and no interference.