What determines if a map can be deleted or not?

From my understanding only the base map are non-removable. All other maps can be uninstalled and reinstall if needed. I own the EU unit, and it come with Europe and US maps. I'm in Asia and i only need SEA map so i uninstall all the Europe and US map and install SEA map only but i notice that the base map is still there but it dont toke up much space since the US and EU map are the one that toke up most of the storage.

That's what I assumed, but I'm unable to remove the africa maps.

Ive check my 1040 under Manage Maps this is what mine looks like i've unchecked all the other country only SEA maps. Basemap cannot be unchecked only Maps under CycleMap can be change. I don't have Topo Maps install.

Under Map Detail only this i see. 

I assume you’re talking about the Map Manager on the Edge itself?

You could try connecting the Edge to your computer and then use Garmin Express to manage the maps. You should be able to remove the Africa map that way.

Actually, the MacOS app & device are disagreeing on what maps are installed.

The app thinks the CycleMap North America & trailforks maps are the only maps installed.

The device thinks that the topoActive Africa map is also installed.

Well that's strange indeed. Does Express show TopoActive Africa as an option even? If so you could try installing it from Express and then, after reconnecting your Edge 1040 to your mac again, removing the same map.