Beginning in the eighteenth century, mapmakers in Europe and the Americas experimented with how lines could represent depth and altitude on a flat page. These lines replaced, but also sometimes mimicked, the earlier convention of drawing small hills and mountains on maps. These techniques, most notably hachure lines and contour lines, met the dual demands that a map be both scientific and visually engaging.
Hachure lines run parallel to the slope. Short, thick strokes show a steep pitch and long, thin strokes show a gradual incline. Mapmakers often combine hachure lines with crosshatching—the network of intersecting lines artists use in printmaking to create shading—to enhance the illusion of depth. Contour lines, in contrast, run perpendicular to the slope. Each contour indicates a consistent change in altitude and is often paired with a numerical key for mathematical precision.