A 'definitive map' is a document that county councils or unitary authorities in England and Wales (excluding inner London boroughs) have to draw up and maintain, to show all the rights of way in their area, and the various rights over these (for instance, whether motor vehicles or cycles can use them).
Definitive maps should be accompanied by a 'definitive statement', which records additional details such as legal widths, gates, etc.
The 1949 National Parks and Access to the Countryside Act obliges authorities to maintain definitive maps; prior to this date it was necessary to go to court to establish whether a particular path was indeed a right of way.