Google maps has now the option to make the map available without data connection. This is great when you are abroad or only use WiFi without a data plan, or just want to safe data for areas you navigate around often.
simply go to the settings menu in google maps,
click on offline areas and download the map, it will automatically estimate the file size.
The map will expire after a certain period, most often a month.
But if you need the storage space earlier you can simply delete the map.