Burnard describes this map as "Ancient map of the first perambulation of Dartmoor. This map is on sheepskin & is supposed to be of early 13th century work".
According to Crossing the first recorded perambulation of Dartmoor was made in 1240 by twelve knights summoned by the Sheriff of Devon.
A perambulation recorded a series of landscape features that defined the boundaries of an area. These defined features could be incorporated in a legal document transferring the designated area to a new owner. The 1240 Dartmoor perambulation described the area given by Henry III to his brother Richard.
Medieval documents that record perambulations are useful to historians as they allow old place names to be accurately located in the modern landscape.