A vast and comprehensive military mapping programme covered the Western Front, combining detail with caution. 

This large scale sectional map is one of 15 adjoining sheets produced by the1st Field Survey Company for the 1st Army, which then occupied the line of front south of the town of Loos in Belgium. The map data was collected through a survey of enemy defences using such techniques as sound ranging and flash spotting. The hand drawn maps were sent to the Ordnance Survey office in Southampton for reproduction, and returned to the front a mere two weeks later. 

This sheet shows the German trenches in red. The British trenches, in blue, have been deliberately distorted so that the information would stay at least partially secret in the event of enemy capture.