While offline navigation is increasingly an edge case I do agree that it offers vast utility in the situations where it's still necessary. Nokia's HERE Drive+

While offline navigation is increasingly an edge case I do agree that it offers vast utility in the situations where it's still necessary. Nokia's HERE Drive+ offers this as its headlining feature on Windows Phone, and Windows Phone comes with offline mapping support built in (to be downloaded on a region-by-region basis). I think the most challenging part of offline mapping is honestly geocoding. Decent vector data for streets is easily available thanks to OSM and learning how to render it and do routing is a fun path down learning well-known algorithms. When you think about it, you're basically reimplementing early 2000s standalone navigation systems like TomTom. But even once I've implemented rendering and routing (and reached early 2000s TomTom parity), I still can't enter "Pizza Hut" and end up at the nearest Pizza Hut. This is where Google excels over other map providers and especially over the existing mobile-phone offline maps solutions like Nokia's - Google's PoI database and search facility is unmatched in my experience. Google even solves for fun problems like locating the closest instance of an intersection between common street names like "23rd and Broadway."