In Delhi, I have been using my Android smartphone with Google Maps for navigation and the only complaint I have is that every time someone calls you the GPS screen goes away!
Moments of pure terror.
But I have a trick for using it offline that I would like to share:
1. Zoom/Rotate/Scroll the map so that the screen has a view of the map area you wish to use.
2. Open the search box, type "ok maps" and click search.
3. It will now go back to map view, and the search box will say "Pre-loading maps __%"
4. Once it has finished pre-loading you can use the map for navigation anytime, without internet! It also saves the Points of Interest (eg. Bus stations) and the Zoomed views!
God knows how much phone data I have saved with this method!