WWI Marginal Information: Base Map Date

Until the last year of the war most British maps were printed by the Ordnance Survey (O.S.) in Southampton, England and then shipped to France where overprint information like trenches was added later. In 1918 an "Overseas Branch" of the Ordnance Survey (O.S., O.B.) was established near St. Omer, France in order to expedite the process in the face of a possible German spring offensive and to avoid potential delays in delivery caused by U-boat activity (see: "Evolution of Mapping on the Western Front"). 

It is important to note that the base map date represents when the base (topographic) information was printed and is not an indication of the currency of the map as the tactical overprint information could be added as much as a year later. Always consult the "trenches corrected to..." date as a more accurate means of assessing the currency of the map. Other base map producers included Field Survey Companies, Battalions, Topo Sections, etc. The War Office (W.O.) also produced maps but only of a very small scale (usually 1:100,000 or smaller).