How to download Maps for Apple maps? How does one cache map data to enable GPS navigation without network access?  I would like to cache maps before visiting an island.
iOS and macOS cache maps as you browse, so the first step is to visit all the places at the scales you wish so your system has a chance to cache the content. 

I’m not aware of a way to force or pin these, so you might need a dedicated map if you have to be sure you have a complete offline map data.