French trenchmap of the area which is crossed by the A19 motorway [Région de Merckem-Ypres, 5 May 1916, 1:20.000].
Note that the enemy lines are marked in blue

In a primary phase of field research, the most important sectors of the front lines were mapped using French, British and German trenchmaps. Surface indications such as trenches, barbed wire entanglements, metre gauge railways, bunkers and shelters were drawn in a G.I.S. Another map was generated indicating altitude, clearly showing the tactical advantage the Germans had at Pilckem Ridge.