iPad mini4 wifi only, so no GPS in it. Try at home.
Idea is to check what make a map appear on the map display with no internet connection.
- Tried to download off-line maps for Google Maps
- Airplane mode on.
- Google Maps shows the off-line mode downloaded, fine.
- Start Go4 app.
- Enter Device.
- Map is dark grey and I have the icon of last Spark position (at home).
- Try to zoom in/out -> stays grey.
- Try to press several time the compas -> stays grey.
- Tried each maps type -> stays grey.
Conclusion it fail by using off-line google maps, it don't seems to share its maps with Go4.
On my IPad there is also a TomTom maps app (don't see any off-line stuff in it) but they seems not related to the one Go4 uses.
See if we can see some cached maps:
- Go4 app
- Back to main menu, go to flight records.
- Display the first one (was far from my home).
- Map is also grey.
- Try to replay it, map remain grey.
- Tried with several (not near my home), no map.
- Now select a flight record near my home and display it.
- Now I see a part of cached (~3km x 3km) my around my home, start point was out of this cached map. So there is something cached.
- Exit flight record and enter device again.
- Map is still grey but there is no more grid and Spark position.
- Turn on the Spark and connect RC using OTG, so iPad remains in airplane mode
- Spark is connected (video) but still map is grey.
- Get GPS home point updated.
- Map still grey whatever icons pressed, zoomed...

- I exited completely Go4 and restarted it.
- Bingo the Spark icon is on the map and if I zoom a little, the cached map appear.
So now, the question is what can be simplified in these steps.
- I kept the Spark and RC connected as I don't think it matter.
- Exit Go4 app and restarted the iPad.
- Connect RC to iPad, launch Go4.
- Spark icon is here, DJI NFZ are here, but NO MAP, it is grey.
- PRESSED the compas icon several time and it comes (thanks @msinger for the tip).
Let's try one more time, everything off, iPad was in airplane mode before turned off.
- Spark ON, RC ON, they are linked.
- Start iPad.
- First try without GPS lock on Spark.
- Connect OTG cable to iPad.
- Grey map, I have a Spark icon, no NFZ disks.
- Zoomed in-out, pressed 2-3 times the compass at each zoom level and BINGO, cached area is displayed.
So this is repeatable. It is only non-intuitive as it is really trial and error. The first press on compas before any zooming, didn't bring anything. Only the combination of both worked; my guess.
Last test without the Spark turned on, only the iPad.
- Power-up iPad, still in airplane mode.
- Start Go4 app, Enter Device.
- Grey map, no Grid, no Spark icon, no NFZ disks.
- Try zoom/compass buttons, no luck.
- Exit to main, go to flight records. Seems only 1 flight record near my home show a cached map.
- Back into the Device.
- Now there is Grid and a Spark icon, no NFZ disk.
- Playing again with the zoom/compass button and finally the cached map is back.
My observations:
- Off-line maps are a pain on ios. Maybe having the cell version with GPS could help ???
- The last or current home point must be displayed on the map with a grid shown. Displaying a flight record near expected position seems to restore it.
- It is not needed that the Spark got GPS sync.
- It is not needed to be connected to the Spark.
- You can get cached map when off-line only for the area where the Spark position is shown on the map. Not checked if you can cache in advance.
- The map area should have been already displayed previously (internet needed), maybe there is some duration for such cached map. The use of flight records map could help if there is no Spark home point icon on the map.
- If you can see (if they are enabled) NFZ disk, then Go4 want to display a map.
- Pressing the compas several times display the map if previous conditions are met (maybe there are more).
- Seems that the cached map in Go4 is related to last Spark position and not to all the place you have been.
- NFZ disk appear only when Spark report GPS position.
- If map is loaded with internet before a flight at a given location, will it be cached for a flight some days after at same location?
- Can Go4 handle more than one map like that ?
- How to cache map in advance for a given location.
Next steps will be:
Sorry, long post but it is really trial/error and try to get a logic out of that, my 5c