Determining Relief and Elevation (MGRS)

Your military map shows something important ordinary maps do not. This is elevation and relief—the slopes, hills, and valleys. You have already learned about locating points, measuring distances, and finding the right direction. But, you should also check hills and valleys along the direction you intend to travel before you start. Elevation of a point on the earth’s surface is the vertical distance it is above or below sea level. Relief is the representation (as depicted by the mapmaker) of the shapes of hills, valleys, streams, or terrain features on the earth’s surface. There are several methods used by mapmakers to depict relief and elevation of the terrain. Contour lines are the most common method used on a standard military map.

Contour Lines

Contour lines are shown as brown lines on a map. Each line depicts the height above sea level. Contour lines never cross one another. Printed at the bottom of the map is the contour interval, which is the difference in height (elevation) between one brown line and the one next to it. On a map with a scale of 1:50,000, the contour interval is usually 20 feet.

This would make point A 80 feet lower than point B (image below). You can determine this because every fifth line is heavier than the rest and has a number that gives its elevation. You could also get an idea of how steep the slope is if you knew the ground distance between point A and point B.

navigation_contour_lines_and_intervals
The rate of rise or fall of a terrain feature is known as its slope. Contour lines widely spaced show a gentle slope; closer contour lines show a steeper slope. The figure below shows how the same hill would look from the ground. Note that side A would be the easier side to climb.

navigation_determining_slope

When the contour lines are close together at the top of a hill, the hilltop is pointed. The hilltop is flat when the contour lines are widely spaced at the top (image below).

navigation_hilltop_contour_lines
Contour lines across a stream always come together in a V-shape (image below).

navigation_contour_lines_stream

The legend on the map shows water as blue. To determine the direction that the water is flowing, look at the contour lines. The Vshape always points upstream or toward high ground. So looking for a stream is a good way to find valleys.

NOTE: Remember to look at the slope (close contour lines equal a steep slope) before following a valley.

Sometimes contour lines show two hilltops fairly close together. The lower terrain between the two hilltops is called a saddle (image below).

navigation_contour_lines_saddle

If you are in a saddle, there is high ground in two opposite directions and lower ground in the other two directions. A saddle is normally represented as an hourglass shape. Going through a saddle is sometimes the easiest route to use to get beyond the two hills. Of course, you would not want to go through a saddle if the enemy was on the hills.

Another terrain feature you should be familiar with is a ridge (image below). A ridge is a fairly long, narrow section of terrain. If you are standing on a ridge, the ground will go uphill in one direction and downhill in the other three. Contour lines that form a ridge tend to be either U- or V-shaped. The closed end of the contour line points away from high ground. The path of the ridge, depending on your geographic location, may be either an almost unnoticeable slope or a very obvious incline.

navigation_contour_lines_ridge

You can also use contour lines to determine the line of sight from one point to another. For example, you are at point A and you want to see point B. To determine the line of sight, draw a line from point A to point B on your map (image below). Note that it crosses some contour lines with higher elevation than both points. Therefore, you know you will not be able to see point B.

navigation_line_of_sight

Remember that a contour line is a brown line on your map that connects points of the same elevation. You can find the contour interval in the margin at the bottom of your map. The heavy brown lines (every fifth one) have the elevation printed on them. You can tell from looking at your map what the slopes, hills, and valleys will look like on the ground.

 

[Continue to Types of Slopes]

**Information adapted from the United States
(U.S.) Army Training Support Centers (TSCs)
Graphic Training Aid (GTA) GTA 05-02-013,
How To Avoid Getting Lost.