All of Great Britain in OS Explorer 1:25k mapping for use on your OS Aventura or OS Horizon GPS Device in one massive download. This is all of our most detailed mapping for GB in a single file. Due to the size of this map, you will need an OS GPS device with SD card capabilities, plus an SD card of at least 32GB capacity. Once purchased, you can immediately log in to your 'My OS GPS' page, and download to your device. You can add the mapping to up to three different devices registered to your account.