It seems like 3G or 4G coverage disappears when you need it most: lost and relying on Google Maps but with no signal. Now Google Maps (for Android) allows you to download a whole area (city, county, country) of the world to your phone and the next time connectivity drops, it will carry on as if still online for both search and navigation purposes.

The app will detect this even if it’s spotty connectivity rather than no signal and as soon as a connection is found it will go back online. It will also wait for wifi to download these maps rather than eat up your data allowance.

This has been in preview for a while but is now integrated into the latest update of Google Maps for Android and is coming soon for iOS. Possibly the best Maps update in a long time.

https://googleblog.blogspot.ie/2015/11/navigate-and-search-real-world-online.html