Pilot alert !! Free stuff:

There's an off-line map application that works great in Europe and South America. (never tried it in Asia). Its called CityMaps2Go.

Its good overseas because you can use the map without using roaming cellular data. Works the same in the USA if you don't have unlimited data.

They are giving it away free just for today. Normally $2.99

Download London, Paris, Rome, Sao Paulo, etc and you're good to go.