The Manual of Map Classification and Cataloguing, known colloquially as the ‘Parsons’ classification, is a geographic-based scheme for structuring a map collection using a sequence of alphanumeric classes and subdivisions. The system was published in 1946 after being devised by Captain Edward J.S. Parsons RE, the inaugural Curator of Maps at the Bodleian Library, University of Oxford. Although originally adopted by Parsons within the map collection of the British War Office, the system was later used to classify the Bodleian’s own map collections, where it remains the basis of the organization of over two million maps, atlases and cartographic books today. This paper explores how the role of the Parsons classification within the Bodleian Library has changed significantly since its genesis in the 1940s. It then outlines recent work undertaken at the library to consolidate and digitize the system so that it better serves a map collection whose infrastructure is now largely digital.