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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.
(c) Rotate the map and compass in the direction of the
declination diagram.
(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. 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. 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. 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. 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.
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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.
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 several field-expedient methods.
Figure 11-6. Field-expedient method.
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From 'Map Reading and Land Navigation', a public domain work published
by the U.S. Department of Defense. |
