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. It uncovers the key clandestine workings of imperial secrets, state secrecy, wider secrets within societies and more recent concepts of personal privacy. Combining the intrigue, excitement and danger that drives human fascination with secrets and the peculiar revelatory thrill that maps give us, it is an essential story with an unsettling edge.