You can download Cartograph Maps here The manual is very easy to understand.
Connect your phone your computer via a USB cable.Upload the maps to your folder of choice. Open up your file manager and navigate to that folder. Now "long press" on the map file you wish to install and a context menu should appear. Tap the Open With link and another menu will appear, then select Cartograph Maps.

Open the app and tap the menu in the top right hand corner. The apps menu will display, tap the Maps menu..

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When you go back to the home screen to view the map you may not see it as the app may have set the zoom at 500km. At the bottom of screen you should see a scale showing the kilometres.
Tap on the menu at the top right again and go to Maps. Long press on the active map and a menu will appear and tap on the Load map in default position. Go back to the map screen and zoom in on the cross hairs and the map will come into veiw.