Map sheet number 172 in the OS Explorer series covers High Wycombe, Maidenhead, Rickmansworth, Gerrards Cross, Northwood, Slough, Uxbridge, Hillingdon, Amersham, Chorleywood, Ruislip & Marlow, the eastern Chiltern Hills & the Thames Path. With this map you will receive a code for use on your i OS or Android smartphone or tablet. Find our more at Mobile Download FAQ. The OS Explorer map for Chiltern Hills East is available in both the standard paper version & weatherproof ' Active' version.