sentences:  A trench map consisted of a base map that showed roads, towns, rivers, forests and so on, over-printed with trenches; red for German, blue for British.Early in 1918 these colours were reversed to come into line with French practice, so that red would henceforth refer to British trenches and blue to German ones.To add to the confusion, some trench maps were printed with all the trenches of the same colour.