Launch Google Maps from your Springboard.
Frame the map area you would like to save for offline use. Make sure it's not too big!
In the search bar input Ok maps and click the blue Search button at the bottom right of the keyboard.
You will now be informed that Google is Pre-loading map....
Once the caching is complete you will be returned to the map and a message at the bottom of the screen will inform you that "The on-screen map area has been cached."