The contour interval on a topographic map is the vertical distance between one contour line and the next.

At the beginning of the war some of the only maps available of France had been produced in the 1880s at a scale of 1:80,000 and had hachures instead of contour lines to indicate changes in elevation. Since artillery had to be concealed in order to avoid being hit by enemy artillery, gunners had to fire blindly based on distance and elevation information provided by maps. For artillery purposes these exisitng maps were totally inadequate.

An attempt was made to overlay contours onto these maps with hachures but it was soon decided that new maps would have to be produced. The most common contour intervals on WWI maps are 5 and 10 metres although some Belgian 1:10,000 scale maps had 1 metre intervals.