Download offline google maps before outgoing is a good idea if you sometimes have poor mobile connection or the mobile data connections is very expensive, the following three free software could download maps from Google Map, OpenStreetMap, CloudMade, or Yahoo Maps.
1) Offline Maps( Windows )
Offline Maps is a free program which provides you the ability to download tiles from Google Maps and Openstreetmap.
The application provides following functionality to its users:
1, The ability to download tiles to a folder on your computer of a given zoomfactor along a path.
2, The ability to view the downloaded tiles in the application.
3, The ability to draw a path on the map and save that path to a file.
4, The ability to receive data from a GPS device and position the map at the points received from the device.
2) Gmapcatcher( Linux, Windows, Mac OSX )
GMapCatcher is an offline maps viewer. It downloads tiles automatically from many providers such as: CloudMade, OpenStreetMap, Yahoo Maps, Google Map. It displays them using a custom GUI. User can view the maps while offline. GMapCatcher doesn’t depend on google-map’s java scripts so it should work even if google changes them. It also provides a downloading tool.
GMapCatcher is written in Python 2.6, can run on Linux, Windows and Mac OSX.
3) MapDroyd( Android )
Simply carry your individual maps offline in your pocket, always at your fingertips. Other than similar offline map applications (like offmaps, bigplanet, etc.) MapDryod does not store cached maps images or tiles! Our MicroMap format represents a fully navigable vector-based street map.