Secrets and maps are a match made in heaven. A Second World War military plan of a cave system covered with red stamps, a tatty hand-drawn treasure map marked with an ‘X’, or even your personal phone screen showing a precise ‘blue dot’ location. These maps contain confidential, coded, precious or private locational information and have, as a result, been hidden away or even falsified to preserve the advantage of ownership. This beautifully illustrated and deeply original book tells the story of how maps, secrets and the data they betray, have come together in western culture over the past six centuries.