Series Number Id: UNKNOWN. Sheet number: part of sheet 28. Map showing German map grids. In green overprint, "Diagram showing German grid and co-ordinate systems in use opposite [British] Fourth Army Front. Note, that four inches from the bottom of the sheet grid system changes. N. of this a Belgian system based on Brussels is used. S. of this the projection is the same as that used by the French, based on Paris as origin." Grey detail and squaring (without letters and numbers). Covers all of Ypres Salient, from Merckem in the north to Armentieres in the south and Menin in the east. Ypres is in left centre. "[Fourth] Field Survey Coy. R.E. (3039) 29-12-17 [followed in green overprint by] (8432)"., Location: Research Collections; Fonds: WW1 Trench Maps: France; Box number: PC23; envelope_number: 708.