He began work in the Map Room of the British Museum upon his return from military service in 1945 and in 1950 became the Superintendent, in which post he continued until his retirement in 1967.
He was the General Editor of Imago Mundi, the major journal in the field of the history of cartography, from 1957 to 1970.
[citation needed] He was Chair of the Working Group on Early Maps of the International Geographical Union from 1961.
He was also a member of the Académie Internationale d'Histoire des Sciences and of various other societies concerned with history, geography, archaeology, bibliography and archives.
During a sabbatical leave in 1962–63, he served as consultant and Acting Map Curator at Harvard University in the Widener Library.