Navigation Methods

7-47. There are three primary means of navigation generally available to the isolated person: global positioning system (GPS), dead reckoning, and terrain association. .

Global Positioning System

7-48. The GPS is a space-based, global, all-weather, continuously available, radio positioning navigation system. It is highly accurate in determining position location derived from signal triangulation from a satellite constellation system. It is capable of determining grid and geographic coordinates (i.e. latitude and longitude) as well as altitude of the individual user. It is fielded in handheld, man pack, vehicular, aircraft, and watercraft configurations.

7-49. The GPS receives and processes data from satellites on a simultaneous or sequential basis. It measures the velocity and range with respect to each satellite, processes the data in terms of an earth-centered, earth-fixed coordinate system, and displays the information to the user in geographic or military grid coordinates. There are several considerations for the employment of GPS by the isolated person:

• GPS has an electronic compass and the ability to store waypoints and enter routes of movement to follow. As an electronic device, it is vulnerable to enemy jamming, spoofing and interference.
• Protect the GPS and conserve battery life to increase its operational life during isolation.
• Zero out the GPS prior to capture to mitigate its exploitation value.
• Use GPS in conjunction with other navigation tools to minimize the chances of becoming lost or unable to correctly execute ISG/ EPA.

Dead Reckoning

7-50. Dead reckoning consists of two fundamental steps. The first step is to use a protractor and graphic scales to determine the direction and distance from one point to another on a map. The second step is to use a compass and some means of measuring distance to apply this information on the ground. In other words, it begins with the determination of a polar coordinate on a map and ends with the act of finding it on the ground.

7-51. Dead reckoning along a given route is the application of the same process used by a mapmaker to establish a measured line of reference upon which to construct the framework of the map. Resection or intersection can be easily undertaken at any time to either determine or confirm precise locations along or near their route. Between these position fixes, isolated persons can establish their location by measuring or estimating the distance traveled along the azimuth being followed from the previous known point. They might use pacing, a vehicle odometer, or the application of elapsed time for this purpose, depending upon the situation.

7-52. Most dead reckoned movements do not consist of single straight-line distances because the tactical and navigational aspects of the terrain, the enemy situation, natural and manmade obstacles, time, and safety factors cannot be ignored. Another reason most dead reckoning movements are not single straight-line distances is because compasses and pace counts are imprecise measures. Error from them compounds over distance; therefore, isolated persons could soon be far from their intended route even if they performed the procedures correctly. The only way to counteract this phenomenon is to reconfirm the location by terrain association or resection. Routes planned for dead reckoning generally consist of a series of straight-line distances between several checkpoints.

7-53. There are two advantages to dead reckoning. First, dead reckoning is easy to teach and learn. Second, it can be a highly accurate way of moving from one point to another if done carefully over short distances, even where few external cues are present to guide movements.

7-54. During daylight, across open country, along a specified magnetic azimuth, isolated persons should never walk with the compass in the open position and in front of them. Because the compass will not stay steady or level, it does not give an accurate reading when held or used this way. Begin at the start point and face with the compass in the proper direction, then sight in on a landmark located on the correct azimuth to be followed. Close the compass and proceed to that landmark. Repeat the process as many times as necessary to complete the straight-line segment of the route.

7-55. The landmarks selected for these purposes are called steering marks, and their selection is crucial to success in dead reckoning. Steering marks should never be determined from a map study. They are selected as the march progresses and are commonly on or near the highest points visible along the azimuth line being followed. They may be uniquely shaped trees, rocks, hilltops, posts, towers, and buildings—anything that can be easily identified. If isolated persons do not see a good steering mark to the front, they might use a back azimuth to some feature behind them until a good steering mark appears out in front. Characteristics of a good steering mark include the following:

• It must have some characteristics, such as color, shade of color, size, or shape (preferably all four), that will assure isolated persons that it will continue to be recognized as they approach it.
• It is the most distant object available along the line of the march. This enables isolated persons to move farther with fewer references to the compass. If there are many options, they should select the highest object. A higher mark is not as easily lost to sight as is a lower mark that blends into the background as it is approached. A steering mark should be continuously visible as an isolated person moves toward it.
• A steering mark selected at night must have even more unique shapes than one selected during daylight. As darkness approaches, colors disappear and objects appear as black or gray silhouettes. Instead of seeing shapes, only the general outlines are visible that may appear to change as they move and objects must be seen from slightly different angles.

7-56. Dead reckoning without natural steering marks is used when the travel area is devoid of features, or when visibility is poor. At night, it may be necessary to send a member of the unit out in front of the unit’s position to create steering marks in order to proceed. The position should be as far out as possible to reduce the number of chances for error during movement. Arm-and-hand signals or a radio may be used in placing the isolated person on the correct azimuth. After being properly located, move forward to this position and repeat the process until some steering marks can be identified or until the objective is reached.

7-57. When handling obstacles and detours on the route, follow these guidelines:

• When an obstacle forces isolated persons to leave their original line of march and take up a parallel one, always return to the original line as soon as the terrain or situation permits.
• To turn clockwise (right) 90°; 90° must be added to their original azimuth. To turn counterclockwise (left) 90° from their current direction, 90° must be subtracted from their present azimuth.
• When making a detour, be certain that only paces taken toward the final destination are counted as part of the forward progress. The forward progress paces should not be confused with the local pacing that takes place perpendicular to the route in order to avoid the problem area and in returning to the original line of march after the obstacle has been passed.

7-58. Highly accurate distance estimates and precision compass work may not be required for a deliberate offset technique if the destination or an intermediate checkpoint is located on or near a large linear feature that runs nearly perpendicular to the direction of travel. Examples include roads or highways, railroads, power transmission lines, ridges, or streams. In these cases, isolated persons should apply a deliberate error (offset) of about 10° to the azimuth they planned to follow and then move, using the lensatic compass as a guide, in that direction until they encounter the linear feature. They will know exactly which way to turn (left or right) to find their destination or checkpoint, depending upon which way they planned their deliberate offset.

7-59. Because no one can move along a given azimuth with absolute precision, it is better to plan a few extra steps than to begin an aimless search for the objective once reaching the linear feature. This method also copes with minor compass errors and the slight variations that always occur in the earth’s magnetic field.

7-60. There are disadvantages to dead reckoning. The farther the movement by dead reckoning without confirming the position in relation to the terrain and other features, the more errors that will accumulate in the movements. Therefore, isolated persons should confirm and correct their estimated position whenever they encounter a known feature on the ground that is also on the map. Periodically, complete a resection using two or more known points to pinpoint and correct their position on the map. Pace counts or any type of distance, measurement should begin anew each time their position is confirmed on the map.

Terrain Association

7-61. The technique of moving by terrain association is more forgiving of mistakes and far less time-consuming than dead reckoning. It best suits those situations that call for movement from one area to another. Once an error has been made in dead reckoning, the isolated person is off the track. However, errors made using terrain association are easily corrected, because isolated persons are comparing what they expected to see from the map to what they do see on the ground.

7-62. Errors are anticipated and will not go unchecked. Isolated persons can easily make adjustments based upon what they encounter. Periodic position fixing through either plotted or estimated resection will also make it possible to correct movements.

Identifying and Locating Selected Features

7-63. Being able to identify and locate selected features, both on the map and on the ground, are essential to the success in moving by terrain association. The following rules may prove helpful:

• Be certain the map is properly oriented when moving along the route and use the terrain and other features as guides. The orientation of the map must match the terrain or it can cause confusion.
• When locating and identifying features to be used to guide movement, look for the steepness and shape of slopes, the relative elevations of various features, and the directional orientations in relation to the isolated person’s position and to the position of other features that can be seen.
• Make use of the additional cues provided by hydrography and vegetation.

Using Handrails, Catching Features, and Navigational Attack Points

7-64. The following paragraphs discuss how to use handrails, catching features, and attack points to determine direction.

Handrails

7-65. Handrails are linear features, such as roads or highways, railroads, power transmission lines, ridgelines, or streams that run roughly parallel to the isolated person’s direction of movement. Instead of using precision compass work, isolated persons can rough compass (using the linear feature to follow the general compass direction) without the use of steering marks for as long as the feature travels with them on their right or left. It acts as a handrail to guide the way.

Catching features

7-66. When isolated persons reach the point where either their route or the handrail changes direction, they must be aware that it is time to go their separate ways. Some prominent feature located near this point is selected to provide this warning. This is called a catching feature; it can also be used to tell when they have gone too far, acting as a backstop.

Navigational attack points

7-67. The catching feature may also be the isolated person’s navigational attack point; this point is the place where area navigation ends and point navigation begins. From this last easily identified checkpoint, move cautiously and precisely along a given azimuth for a specified distance to locate the final objective. The selection of this navigational attack point is important. A distance of about 500 meters or less is most desirable.

Combining Techniques

7-68. The most successful navigation is obtained by combining the techniques described above. Constant orientation of the map and continuous observation of the terrain in conjunction with compass-read azimuths, and distance traveled on the ground compared with map distance, when used together, make reaching a destination more certain. Isolated persons should not depend entirely on compass navigation or map navigation.

Navigation Fundamentals

7-69. Prior to navigation, the isolated person will orient 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.

Using a Compass

7-70. 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. Two techniques are used. To determine the direction of the declination and its value from the declination diagram on the map. Place 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.

Note. Maps are drawn to a specific representation of a piece of the earth’s surface. This representation is oriented or pointed to true north or in the direction of the North Pole located along the earth’s rotational axis. The compass points to magnetic north or the north magnetic pole. This is in the general direction of true north, but depending on where the map is drawn to on the earth’s surface there is a variation between the two. This is an easterly or westerly variation and will be represented in different degrees. The declination diagram in the map’s information section will provide the angular relationship between true north and magnetic north. This allows for making an adjustment to the map that is known as orienting the map.) The best way to orient a map is with a compass. For use of a lensatic compass, see TC 3-25.26.

Note. Use caution to ensure nothing (metal, mine and ore) in the area will alter the compass reading.

7-71. The lensatic compass has a needle with a north direction marked on the bottom inside of the compass. A button or wrist compasses may have floating dials or floating needles. To determine the heading, line up the north-seeking arrow over 360° by rotating the compass, then read the desired heading. Orienting a map with a floating needle compass is similar to the method used with the floating dial. The only exception is with the adjustment for magnetic variation. If magnetic variation is to the east, turn the map and the compass to the left (the north axis of the compass should be aligned with the map north) so that the magnetic north-seeking arrow is pointing at the number of degrees on the compass which correspond with the angle of declination. See figure 7-13.

Map Orientation

7-72. When a compass is not available, map orientation requires a careful examination of the map and the ground to find linear features common to both, such as roads, railroads, and power lines. The map is oriented by aligning a feature on the map with the same feature on the ground. Orientation by this method must be checked to prevent the reversal of directions, which may occur if only one linear feature is used. This reversal may be prevented by aligning two or more map features (terrain or manmade). If no second linear feature is visible but the map user’s position is known, a prominent object may be used. With the prominent object and the user’s position connected with a straight line on the map, the map is rotated until the line points toward the feature.

7-73. If two prominent objects are visible and plotted on the map and the position is not known, move to one of the plotted and known positions, place the straightedge or protractor on the line between the plotted positions, and turn the protractor and the map until the other plotted and visible point is seen along the edge. The map is then oriented (see figure 7-14 on page 7-20).

Terrain Features

7-74. Major terrain features include—

• Hills. A hill is an area of high ground. From a hilltop, the ground slopes down in all directions. A hill is shown on a map by contour lines forming concentric circles. The inside of the smallest closed circle is the hilltop (see figure 7-15).

• Saddles. A saddle is a dip or low point between two areas of higher ground. A saddle is not necessarily the lower ground between two hilltops; it may be simply a dip or break along a level ridge crest. In a saddle, there is high ground in two opposite directions and lower ground in the other two directions. It is normally represented as an hourglass (see figure 7-16 on page 7-21).

• Valleys. A valley is a stretched-out groove in the land, usually formed by streams or rivers. A valley begins with high ground on three sides and usually has a course of running water through it. In a valley, three directions offer high ground, while the fourth direction offers low ground. Depending on its size and where a person is standing, it may not be obvious that there is high ground in the third direction, but water flows from higher to lower ground. Contour lines forming a valley are either U-shaped or V-shaped. To determine the direction water is flowing, look at the contour lines. The closed end of the contour line (U or V) always points upstream or toward high ground (see figure 7-17).

• Ridges. A ridge is a sloping line of high ground. On the centerline of a ridge, there will normally be low ground in three directions and high ground in one direction with varying degrees of slope. If isolated persons cross a ridge at right angles, they will climb steeply to the crest and then descend steeply to the base. When they move along the path of the ridge, depending on the geographic location, there may be either an almost unnoticeable slope or a very obvious incline. Contour lines forming a ridge tend to be U-shaped or V-shaped. The closed end of the contour line points away from high ground (see figure 7-18, page 7-22).

• Depressions. A depression is a low point in the ground or a sinkhole. It could be described as an area of low ground surrounded by higher ground in all directions, or simply a hole in the ground. Usually only depressions that are equal to or greater than the contour interval will be shown. On maps, depressions are represented by closed contour lines that have tick marks pointing toward low ground (see figure 7-19).

7-75. Minor terrain features include—

• Draws. A draw is a stream course that is less developed than a valley. In a draw, there is essentially no level ground; therefore, there is little or no maneuver room within its confines. In a draw, the ground slopes upward in three directions and downward in the other direction. A draw could be considered as the initial formation of a valley. The contour lines depicting a draw are U-shaped or V-shaped, pointing toward high ground (see figure 7-20 on page 7-23).

• Spurs. A spur is a short, continuous sloping line of higher ground, normally jutting out from the side of a ridge. A spur is often formed by two roughly parallel streams cutting draws down the side of a ridge. The ground will slope down in three directions and up in one. Contour lines on a map depict a spur with the U or V pointing away from high ground (see figure 7-21).

• Cliffs. A cliff is a vertical or near vertical feature; it is an abrupt change of the land. When a slope is so steep that the contour lines converge into one “carrying” contour of contours, this last contour line has tick marks pointing toward low ground). Cliffs are also shown by contour lines very close together and, in some instances, touching each other (see figure 7-22 on page 7-24).

7-76. Supplementary terrain features include—

• Cuts. A cut is a manmade feature resulting from cutting through raised ground, usually to form a level bed for a road or railroad track. Cuts are shown on a map when they are at least 10 feet high, and they are drawn with a contour line along the cut line. This contour line extends the length of the cut and has tick marks that extend from the cut line to the roadbed, if the map scale permits this level of detail.
• Fills. A fill is a manmade feature resulting from filling a low area, usually to form a level bed for a road or railroad track. Fills are shown on a map when they are at least 10 feet high, and they are drawn with a contour line along the fill line. This contour line extends the length of the filled area and has tick marks that point toward lower ground. If the map scale permits, the length of the fill tick marks are drawn to scale and extend from the base line of the fill symbol.

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