When travelling in a new city, it is often difficult to find your way and when you get lost always great to be able to open Google maps and re-orientate yourself and get back on track.
However mobile data roaming is expensive, and taking that path can end up costing you. I was travelling in Thailand in 2012 (before you could download offline maps) and we got lost trying to find a restaurant called Nikki Beach in Koh Samui (we had followed the websites directions but kept going around in circles) and ultimately I opened up Google Maps using roaming data to navigate us the last few miles. Lets just say the data usage cost me more than my lunch.
Google now allows you to download an area offline which will remain cached in your phone for 30 days.
Most maps are 40-60 MB in size. To download an offline area, simply open Google Maps, type in the city /areas name in the search bar and once the area has loaded, hit the menu key (three horizontal lines on the left of the search bar), select “Offline Area” hit the + key at the bottom of the screen to add.
Offline Area’s will only download on a Wifi Connection.
See the detailed help article on Google Support on how to use Google maps offline