Series Number Id: UNKNOWN. Sheet number: 20, 28, 36. Second Army area air reconnaissance (?) map, 1915. [Second Army area and part of First]. Grey and blue Ordnance Survey or War Office administrative base map, with railways in black, covering front area from north of Clerken (north of Houthulst Forest) to Givenchy, Cuinchy and La Bassée, and as far east as Roulers, Menin, Tourcoing, Roubaix, and Lille. Red overprint with British 1:40,000 sheetlines and lettered and numbered squaring system (revised system of squaring, introduced December 1914). Possibly produced for air reconnaissance purposes. The first such grey and blue base map was apparently produced about mid-1915. Stone/plate for red overprint registered with needles., Location: Research Collections; Fonds: WW1 Trench Maps: France; Box number: PC19; envelope_number: 589.