Part One
  Map Reading


  Reading Topographical Maps Introduction 1. HOME

  Topographical Maps - Definition, Purpose and Categories 2. Maps

  Information in the margins of an army map 3. Marginal Information    and Symbols

  Latitude, Longitude and Other Methods to Locate Points on Topographic Maps 4. Grids

  Translating Distance on a Topographic Map to Distance on the Ground 5. Scale and Distance

  Grid North, Azimuth, Declination And Other Concepts Used To Find Direction With Topographic Maps 6. Direction

  Overlays - Used Primarily In Army Map Reading 7. Overlays

  Aerial Photographs - Supplements And Substitutes For Topographic Maps 8. Aerial Photographs

 Part Two
  Land Navigation


  Using Compass, GPS, Sun, Shadows, and Stars in Land Navigation 9. Navigation Equipment    and Methods

  Reading The Shape Of The Land In Topographic Maps 10. Elevation and Relief

  Orienting and Navigating With Topographic Maps 11. Terrain Association

  Mounted Land Navigating With Motorized Vehicles 12. Mounted Land    Navigation

  Land Navigation In Different Types of Terrain 13. Navigation in    Different Types of    Terrain



  Sketching Topographic Maps A. Field Sketching

  Folding Topographic Maps B. Map Folding     Techniques

  Units of Measure and Conversion Factors Used in Reading Topographic Maps C. Units of Measure and      Conversion Factors

  Units of Measure and Conversion Factors Used in Reading Topographic Maps D. Joint Operations      Graphics

  US Army Training Material for Map Reading and Land Navigation E. Exportable Training      Material

  Orienteering F. Orienteering

  US Army M2 Compass G. M2 Compass

  Additional Aids such as Night Vision Goggles and Global Positioning System or GPS H. Additional Aids      (GPS, Night Vision)

  Global Positioning System -  GPS J. Global Positioning      System - GPs

 

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5-3. OTHER METHODS

Determining distance is the most common source of error encountered while moving either mounted or dismounted. There may be circumstances where you are unable to determine distance using your map or where you are without a map. It is therefore essential to learn methods by which you can accurately pace, measure, use subtense, or estimate distances on the ground.

a.   Pace Count. Another way to measure ground distance is the pace count. A pace is equal to one natural step, about 30 inches long. To accurately use the pace count method, you must know how many paces it takes you to walk 100 meters. To determine this, you must walk an accurately measured course and count the number of paces you take. A pace course can be as short as 100 meters or as long as 600 meters. The pace course, regardless of length, must be on similar terrain to that you will be walking over. It does no good to walk a course on flat terrain and then try to use that pace count on hilly terrain. To determine your pace count on a 600-meter course, count the paces it takes you to walk the 600 meters, then divide the total paces by 6. The answer will give you the average paces it takes you to walk 100 meters. It is important that each person who navigates while dismounted knows his pace count.

(1)   There are many methods to keep track of the distance traveled when using the pace count. Some of these methods are: put a pebble in your pocket every time you have walked 100 meters according to your pace count; tie knots in a string; or put marks in a notebook. Do not try to remember the count; always use one of these methods or design your own method.

(2)   Certain conditions affect your pace count in the field, and you must allow for them by making adjustments.

(a)   Slopes. Your pace lengthens on a downslope and shortens on an upgrade. Keeping this in mind, if it normally takes you 120 paces to walk 100 meters, your pace count may increase to 130 or more when walking up a slope.

(b)   Winds. A head wind shortens the pace and a tail wind increases it.

(c)   Surfaces. Sand, gravel, mud, snow, and similar surface materials tend to shorten the pace.

(d)   Elements. Falling snow, rain, or ice cause the pace to be reduced in length.

(e)   Clothing. Excess clothing and boots with poor traction affect the pace length.

(f)   Visibility. Poor visibility, such as in fog, rain, or darkness, will shorten your pace.

b.   Odometer. Distances can be measured by an odometer, which is standard equipment on most vehicles. Readings are recorded at the start and end of a course and the difference is the length of the course.

(1)   To convert kilometers to miles, multiply the number of kilometers by 0. 62.

EXAMPLE:

16 kilometers = 16 x 0. 62 = 9. 92 miles

(2)   To convert miles to kilometers, divided the number of miles by 0. 62.

EXAMPLE:

10 miles = 10 divided by 0. 62 = 16. 12 kilometers

c.   Subtense. The subtense method is a fast method of determining distance and yields accuracy equivalent to that obtained by measuring distance with a premeasured piece of wire. An advantage is that a horizontal distance is obtained indirectly; that is, the distance is computed rather than measured. This allows subtense to be used over terrain where obstacles such as streams, ravines, or steep slopes may prohibit other methods of determining distance.

(1)   The principle used in determining distance by the subtense method is similar to that used in estimating distance by the mil relation formula. The field artillery application of the mil relation formula involves only estimations. It is not accurate enough for survey purposes. However, the subtense method uses precise values with a trigonometric solution. Subtense is based on a principle of visual perspective—the farther away an object, the smaller it appears.

(2)   The following two procedures are involved in subtense measurement:

  • Establishing a base of known length.

  • Measuring the angle of that base by use of the aiming circle.

(3)   The subtense base may be any desired length. However, if a 60-meter base, a 2-meter bar, or the length of an M16A1 or M16A2 rifle is used, precomputed subtense tables are available. The M16 or 2-meter bar must be held horizontal and perpendicular to the line of sight by a soldier facing the aiming circle. The instrument operator sights on one end of the M16 or 2-meter bar and measures the horizontal clockwise angle to the other end of the rifle or bar. He does this twice and averages the angles. He then enters the appropriate subtense table with the mean angle and extracts the distance. Accurate distances can be obtained with the M16 out to approximately 150 meters, with the 2-meter bar out to 250 meters, and with the 60-meter base out to 1,000 meters. If a base of another length is desired, a distance can be computed by using the following formula:

Distance = 1/2 (base in meters)
————————
Tan (1/2) (in mils)

d.   Estimation. At times, because of the tactical situation, it may be necessary to estimate range. There are two methods that may be used to estimate range or distance.

(1)   100-Meter Unit-of-Measure Method. To use this method, the soldier must be able to visualize a distance of 100 meters on the ground. For ranges up to 500 meters, he determines the number of 100-meter increments between the two objects he wishes to measure. Beyond 500 meters, the soldier must select a point halfway to the object(s) and determine the number of 100-meter increments to the halfway point, then double it to find the range to the object(s) (Figure 5-9).

Figure 5-9.  Using a 100-meter unit-of-measure method.

Figure 5-9. Using a 100-meter unit-of-measure method.

(2)   Flash-To-Bang Method. To use this method to determine range to an explosion or enemy fire, begin to count when you see the flash. Count the seconds until you hear the weapon fire. This time interval may be measured with a stopwatch or by using a steady count, such as one-thousand-one, one-thousand-two, and so forth, for a three-second estimated count. If you must count higher than 10 seconds, start over with one. Multiply the number of seconds by 330 meters to get the approximate range (FA uses 350 meters instead).

(3)   Proficiency of Methods. The methods discussed above are used only to estimate range (Table 5-1). Proficiency in both methods requires constant practice. The best training technique is to require the soldier to pace the range after he has estimated the distance. In this way, the soldier discovers the actual range for himself, which makes a greater impression than if he is simply told the correct range.

Factors Affecting Range Estimation Factors Causing Underestimation of Range Factors Causing Overestimation of Range
The clearness of outline and details of the object. When most of the object is visible and offers a clear outline. When only a small part of the object can be seen or the object is small in relation to its surroundings.
Nature of terrain or position of the observer.

When looking across a depression that is mostly hidden from view.

When looking downward from high ground.

When looking down a straight, open road or along a railroad.

When looking over uniform surfaces like water, snow, desert, or grain fields.

In bright light or when the sun is shining from behind the observer.

When looking across a depression that is totally visible.

When vision is confined, as in streets, draws, or forest trails.

When looking from low ground toward high ground.

In poor light, such as dawn and dusk; in rain, snow, fog; or when the sun is in the observerís eyes.

Light and atmosphere

When the object is in sharp contrast with the background or is silhouetted because of its size, shape, or color.

When seen in the clear air of high altitudes.

When object blends into the background or terrain.

Table 5-1. Factors of range estimation.


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Books

Map Reading and Land Navigation 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.

Read a book review of Agincourt

Boat Navigation For The Rest of Us
  Boat Navigation For The Rest of Us

Basic Coastal Navigation
  Basic Coastal Navigation