Map Reading - Orienting the map to the ground for use in land navigation

11-1. ORIENTING THE MAP

The first step for a navigator in the field is orienting the map. A map is oriented when it is in a horizontal position with its north and south corresponding to the north and south on the ground. Some orienting techniques follow:

a. Using a Compass. When orienting a map with a compass, remember that the compass measures magnetic azimuths. Since the magnetic arrow points to magnetic north, pay special attention to the declination diagram. There are two techniques used.

(1) First Technique. Determine the direction of the declination and its value from the declination diagram.

(a) With the map in a horizontal position, take the straightedge on the left side of the compass and place it alongside the north-south grid line with the cover of the compass pointing toward the top of the map. This procedure places the fixed black index line of the compass parallel to north-south grid lines of the map.

(b) Keeping the compass aligned as directed above, rotate the map and compass together until the magnetic arrow is below the fixed black index line on the compass. At this time, the map is close to being oriented.

(d) If the magnetic north arrow on the map is to the left of the grid north, check the compass reading to see if it equals the G-M angle given in the declination diagram. The map is then oriented (Figure 11-1).

Figure 11-1. Topographic Map oriented with 11 degrees west declination.

Figure 11-1. Map oriented with 11 degrees west declination.

(e) If the magnetic north is to the right of grid north, check the compass reading to see if it equals 360 degrees minus the G-M angle (Figure 11-2).

Figure 11-2. Topographic Map oriented with 21 degrees east declination.

Figure 11-2. Map oriented with 21 degrees east declination.

(2) Second Technique. Determine the direction of the declination and its value from the declination diagram.

(a) Using any north-south grid line on the map as a base, draw a magnetic azimuth equal to the G-M angle given in the declination diagram with the protractor.

(b) If the declination is easterly (right), the drawn line is equal to the value of the G-M angle. Then align the straightedge, which is on the left side of the compass, alongside the drawn line on the map. Rotate the map and compass until the magnetic arrow of the compass is below the fixed black index line. The map is now oriented (Figure 11-3).

Figure 11-3. Topographic Map oriented with 15 degrees east declination.

Figure 11-3. Map oriented with 15 degrees east declination.

(c) If the declination is westerly (left), the drawn line will equal 360 degrees minus the value of the G-M angle. Then align the straightedge, which is on the left side of the compass, alongside the drawn line on the map. Rotate the map and compass until the magnetic arrow of the compass is below the fixed black index line. The map is now oriented (Figure 11-4).

Figure 11-4. Topographic Map oriented with 10 degrees west declination.

Figure 11-4. Map oriented with 10 degrees west declination.

NOTE:

1. Once the map is oriented, magnetic azimuths are determined using the compass. Do not move the map from its oriented position since any change in its position moves it out of line with the magnetic north. [See paragraph 11-6b(1).]

2. Special care should be taken whenever orienting your map with a compass. A small mistake can cause you to navigate in the wrong direction.

b. Using Terrain Association. A map can be oriented by terrain association when a compass is not available or when the user has to make many quick references as he moves across country. Using this method requires careful examination of the map and the ground, and the user must know his approximate location (Figure 11-5). Orienting by this method is discussed in detail in paragraph 11-3.

Figure 11-5. Terrain association between a topographic map and the ground.

Figure 11-5. Terrain association.

c. Using Field-Expedient Methods. When a compass is not available and there are no recognizable terrain features, a map may be oriented by any of the field-expedient methods described in paragraph 9-5. Also see Figure 11-6.

Figure 11-6. Field-expedient method for orienting a topographic map with the ground.

Figure 11-6. Field-expedient method.

Return to Terrain Association

Books

Buy the book this website is based on: Map Reading and Land Navigation

This website is based on the US Army Field Manual: "Map Reading and Land Navigation" Buy a copy from Amazon.com to take with you out in the field.

Book Review - Be Expert with Map and Compass

One of the best ways to learn and become proficient in any subject is to find a way to make a game or sport of it. That's exactly what orienteering does! Orienteering began to develop almost 100 years ago in the Scandinavian countries as a fun and effective method for military training in land navigation. Bjorn Kjellstrom was closely involved with the early development of orienteering, and he is the person who introduced the sport to North America. He, along with his brother Alvar, and a friend named Gunnar Tillander, invented the modern orienteering compass. They manufactured and marketed it as the Silva Protractor compass. This compass, along with Bjorn's book Be Expert with Map and Compass, made it much easier for anyone to learn how to use a map and compass.

This book has become the most widely read classic on the subject of map reading, compass use, and orienteering. Over 500,000 copies have been sold in the english language editions alone. There have been very successful editions published in French, Italian, and other languages as well. It is a short (just over 200 pages), easy to read, enjoyable book that can help you to have fun while you learn the subject quickly and effectively.

The book is organized into four main parts, plus a short, useful introduction. Part 1 covers having fun with maps alone. Then, Part 2 covers having fun with a compass alone. Part 3 puts it together and shows you how to have fun with a map and compass together. This section also introduces the game or sport of orienteering. Part 4 covers competitive orienteering for those who would like to compete with others in the sport.

A reproduction of a segment of an actual topographic map is included as a fold-out in the back of the book. It is used together with the "how-to" instructions the book provides. For example, one of the exercises in Part 3 is an imaginary orienteering "hike" that uses the sample map.

If you would like to have one of the best books available on map reading and using a compass, Be Expert with Map and Compass is hard to beat. You can buy a copy from Amazon.com today.

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