The elevation of points on the ground and the reliefof an area affect the movement and positioning of military units. Relief is the representation of the shapes of hills, valleys, streams, or terrain features on the earth's surface. Mapmakers use several methods to depict relief of the terrain. Layer tinting is a method of showing relief by color. Hachures are short, broken lines used to show relief. Relief shading indicates relief by a shadow effect achieved by tone and color. A contour line is an imaginary line on the ground, above or below mean sea levelwhich represents vertical positionsor relief. The elevations and contours are measured from a specific vertical datum plane.