A knowledge of map symbols, grids, scale, and distance provides enough information to identify two points. You locate them, measure between them, and determine the length of time required to travel between them. But what happens if there is a 300-foot cliff between the two points? The map user must also become proficient in recognizing the various landforms and irregularities of the surface of the earth. Then he is able to determine the elevation and differences in the height of all terrain features.

1. DATUM PLANE. This is a reference from which vertical measurements are taken. The datum plane for most maps is mean, or average, sea level.

2. ELEVATION. This is defined as the height (vertical distance) of an object above or below a datum plane.

3. RELIEF. Relief is the representation of the shape and height of landforms and the characterization of the surface of the earth.

The elevation of points and the relief of an area affect the movement and deployment of units by limiting the route of travel, their speed of movement, and the ease or difficulty of attacking or defending an area. Also relief affects observation, fields of fire, cover, concealment, and the selection of key terrain features.