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BST Infantry Skills – Employ a Map and Compass

Employ a Map and Compass

Training Support Package (TSP) for the Marine Battle Skills Test (BST)

 TASK: Employ a map and compass

CONDITION: Given a military topographic map, protractor, and compass

STANDARD: Completing all the performance steps without error
TIME TO TRAIN: 45 minutes

TIME TO TEST: 15 minutes per Marine

PERFORMANCE STEPS:
  1. Describe the marginal information found on a topographical map
  2. Identify terrain features found on a topographical map
  3. Identify what colors represent on a topographical map
  4. Plot a point on a map using the protractor
  5. Determine the six-digit grid coordinate of a specific point on a map
  6. Determine the straight line and/or curved line distance between two points on a map
  7. Determine a back azimuth
  8. Determine the grid azimuth between two points on a map
  9. Convert a grid azimuth to a magnetic azimuth
  10. Convert a magnetic azimuth to a grid azimuth
REFERENCES: TC 3-25.26 – Map Reading and Land Navigation
SUPPORT REQUIREMENTS: Topographic map, protractor, map pens, and a lensatic compass

PERFORMANCE STEP 1:  Describe the marginal information found on a topographical map: sheet name, series name, scale, bar scale, contour interval, declination diagram, adjoining sheets diagram, and legend.

Topographic Map.  A topographic map is a map that portrays terrain features in a measurable way usually through the use of contour lines, as well as the horizontal positions of the features represented.

Marginal Information.  The instructions that are placed around the outer edges of a map are known as marginal information.  This information will provide you with the information necessary to read your map.  However, since all maps are not the same, it becomes necessary to examine all the marginal information carefully, every time a different map is used.

Sheet Name.  Found in two places; center of the upper margin, and the left side of the lower margin. Generally, a map is named after outstanding cultural or geographic feature.

 Series Name.  The map series name is found in the upper left corner of the margin. The name given to the series is generally that of a major political subdivision such as a state within the United States or a European nation.

Scale. The scale is found in the upper left margin after the series name and in the center of the lower margin.  The scale note is a representative fraction, which gives the ratio of a map distance to the corresponding distance on the earth’s surface.  For example, a scale note of 1:50,000 would indicate that the distance covered by one inch on the map would equal 50,000 inches on the actual ground.

Bar Scale. Located in the center of the lower margin, it is used to convert map distance to ground distance. Maps have three or more bar scales, each in a different unit of measure.

Contour Interval. Located in the lower margin.  It states the vertical distance between adjacent contour lines on the map.

Declination Diagram. Located in the lower margin, it indicates the angular relationships of true, grid, and magnetic north.

True North.  A line from any point on the earth’s surface to the North Pole is a true north line. True north is usually represented by a line ending with a star.

Grid North.  This baseline is established by using the vertical grid lines on the map. Grid north may be symbolized by the letters GN.  Anytime you are using a protractor in conjunction with a vertical grid line to determine or plot an azimuth on a map, you must be working with an azimuth measured from grid north.

Magnetic North. The direction to the north magnetic pole is indicated by the north-seeking needle of your lensatic compass. Magnetic north is usually symbolized by a line ending with a half arrowhead. Any time you are using the compass to plan or follow an azimuth in the field, you must be working with azimuths measured from magnetic north.

Using magnetic north or grid north as the baseline, we define grid azimuth and magnetic azimuth.

  1. A grid azimuth is an angle measured in a clockwise direction from grid north.
  1. A magnetic azimuth is an angle measured in a clockwise direction from magnetic north.

Legend.  Located in the lower left margin, it illustrates and identifies the topographical symbols of some of the prominent features on the map. The symbols are not always the same on every map, so the legend must always be referred to when using a map.

PERFORMANCE STEP 2:  Identify terrain features found on a topographical map.

Major Terrain Features. 
  1. Hill. 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 circle is the hilltop.
  2. Ridge. This is a sloping line of high ground. 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.
  1. Saddle. This is a dip or low point between two areas of higher ground. A saddle is normally represented as an hourglass or by figure eight shaped contour lines.
  1. Valley. This is a stretched-out groove in the land, usually formed by streams or 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.
  1. Depression. This is a low point in the ground or a sinkhole. A depression could be described as an area of low ground surrounded by higher ground in all directions, or simply a hole in the ground. On maps, depressions are represented by closed contour lines that have tick marks pointing toward low ground.
Minor Terrain Features.
  1. Finger. A finger is a short continuous sloping line of higher ground, normally jutting out from the side of a ridge. Contour lines on a map depict a finger with a U or V pointing away from high ground.
  1. Draw. A draw is a less developed stream course than a valley. In a draw, there is essentially no ground and, therefore, little or no maneuver room within its confines. The contour lines depicting a draw are U-shaped or V-shaped, pointing toward high ground.
  1. Cliff. A cliff is a vertical or near vertical feature; it is an abrupt change of the land. Cliffs are shown by contour lines very close together and, in some instances, touching each.
Supplementary Terrain Features. 
  1. Cut. A cut is a man-made feature resulting from cutting through high 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.
  1. Fill. Fill is a man-made 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.

PERFORMANCE STEP 3:  Identify what colors represent on a topographical map

To facilitate the identification of features on a map, the topographical and cultural information is usually printed in different colors. These colors may vary from map to map. On a standard large-scale topographic map, the colors used on a map represent certain features:

  1. Black. Indicates cultural (man-made) features, such as buildings and roads.
  1. Blue. Identifies hydrography or water features such as lakes, swamps, rivers, and drainage.
  1. Green. Identifies vegetation with military significance.
  1. Red. Classifies cultural features, such as populated areas, main roads, and boundaries, on older maps.
  1. Brown. Identifies all relief features, such as contours on older edition maps.
  1. Reddish-Brown. The colors red and brown are combined to identify cultural features, all relief features, and elevation, such as contour lines on red-light readable maps.
  1. Other. Occasionally other colors may be used to show special information. These are indicated in the marginal information as a rule.

PERFORMANCE STEP 4:  Plot a point on a map using the protractor.

The map has lines running up and down and side to side. These lines form small squares, 1,000 meters on each side, called grid squares. The lines that form grid square are numbered along the outside edge of your map. No two grid squares will have the same number. The precision of a point location is shown by the number of digits in the coordinates; the more digits, the more precise the location:

  1. 4-digit coordinates label a point to the nearest 1,000 meters
  2. 6-digit coordinates label a point to the nearest 100 meters
  3. 8-digit coordinates label a point to the nearest 10 meters
  4. 10-digit coordinates label a point to the nearest 1 meter

There are three coordinate scales located on your protractor: 1:100,000, 1:50,000 and 1:25,000.  Use the one that corresponds with the scale of the map you are using.  To plot the point 148842, begin by placing the proper coordinate scale of your protractor with the zero-zero point at the lower left hand corner of the grid square 1484.  Then move the protractor right until the number eight on the horizontal scale is aligned with the lower left hand corner of the square.  Finish by finding the number two on the vertical scale and plot the point.

Special care should be exercised when recording and reporting coordinates. Transposing numbers or making errors could be detrimental to military operations.

PERFORMANCE STEP 5Determine the six-digit grid coordinate of a specific point on a map.

To determine the location of point A, we apply the rule “read right, then up”.  The first half of the reported set of coordinate digits represents the left-to-right (easting) grid label, and the second half represents the label as read from the bottom-to-top (northing).

Place the proper coordinate scale of your protractor with the zero-zero point at the lower left hand corner of the grid square that point A is found within.  Move the protractor right until the vertical scale is aligned with the point A.  Point A on the figure below would be recorded as 148842

PERFORMANCE STEP 6: Determine the straight line and/or curved line distance between two points on a map.

Graphic Scales. You may use the bar scale on your map to convert distances on the map to actual ground distance. The bar scale is divided into two parts. To the right of the zero, the scale is marked in full units of measure and is called the primary scale. To the left of the zero, the scale is divided into tenths and is called the extension scale. Most maps have three or more bar scales, each using a different unit of measure. Be sure to use the correct scale for the unit of measure desired:

  1. The graduated straightedge of the lensatic compass is engraved with a graphic scale. This graphic scale represents 6,000 meters of ground distance on a map with a scale of 1:50,000. This distance is divided, by lines, into 100-meter increments.
  1. The coordinate scale on the protractor you have been issued may also be used to determine distance. If a coordinate scale is used to determine ground distance, you must be sure it is at the same scale as the map you are using.
  1. Your choice of graphic scale to use when determining ground distances is unimportant. If properly used, they will all produce the same results. Use whichever form is available to you or is the most practical for the problem at hand.

Determining Straight Line Distance. To determine straight-line distance between two points on a map, lay a straight-edged piece of paper on the map so that the edge of paper touches both points and extends past them. Make a tick mark on the edge of the paper at each point. Remember that the center of the topographic symbol accurately designates the true location of the object on the ground:

  1. To convert the map distance to ground distance, move the paper down to the graphic bar scale, and align the right tick mark (b) with a printed number in the primary scale so that the left tick mark (a) is in the extension scale. For example, if the right tick mark (b) is aligned with the 3,000 meter mark in the primary scale, the distance is at least 3,000 meters.
  1. To determine the distance between the two points to the nearest 10 meters, look at the extension scale. The extension scale is numbered with zero at the right and increases to the left. When using the extension scale, always read it right to left. From the zero to the end of the first shaded square is 100 meters. From the beginning of the clear square to the left is 100 to 200 meters; at the beginning of the second shaded square is 200 to 300 meters. Remember, the distance in the extension scale increases from right to left.
  1. To determine the distance from the zero tick mark (a), estimate the distance inside the squares to the closest tenth. As you break down the distance between the squares in the extension scale, you will see that tick mark (a) is aligned with the 950-meter mark. Adding the distance of 3,000 meters determined in the primary scale, we find that the total distance between (a) and (b) is: 3,000 + 950 = 3,950

Determining Curved Line Distance. To measure distance along a winding road, stream, or other curved line, you still use the straight edge of a piece of paper. In order to avoid confusion concerning the start point and the ending point, a six-digit coordinate, combined with a description of the topographical feature, should be given for both the starting and ending points. Place a tick mark on the paper and map at the beginning point from which the curved line is to be measured. Place a paper strip or other material with a straightedge along the center of the irregular feature, and extend the tick mark onto the paper strip.

Because the paper strip is straight and the irregular feature is curved, the straightedge will eventually leave the center of the irregular feature. At the exact point where this occurs, place a tick mark on both the map and paper strip. Keeping both tick marks together (on paper and map), place the point of the pencil close to the edge of the paper on the tick mark to hold it in place and pivot the paper until another straight portion of the curved line is aligned with the edge of the paper. Repeat this procedure, carefully aligning the straightedge with the center of each feature and placing tick marks on both the map and paper strip each time it leaves the center, until you have the desired distance:

  1. Place the paper strip on a graphic scale and determine the ground distance measured.

PERFORMANCE STEP 7: Determine a back azimuth.

In the simplest terms, an azimuth is a straight line from one point to another. A more complete definition however is that: An azimuth is an angle measured in a clockwise direction from a predetermined base line. Before attempting to determine or follow an azimuth in the field, you must have a clear understanding of each part of this definition.

Determining Back Azimuths. A back azimuth is the opposite direction of an azimuth. It is the same as doing an “about face.” To obtain a back azimuth from an azimuth use the acronym LAMS, (Less Add – More Subtract):

  1. Less than 180 degrees – add 180 degrees.
  2. More than 180 degrees – subtract 180 degrees.
  3. The back azimuth of 180 degrees may be stated as 0 degrees or 360 degrees.

PERFORMANCE STEP 8: Determine the grid azimuth between two points on a map.

 Determining Grid Azimuths. To determine the direction from one point to another on the map (grid azimuth) you need to perform the following steps:

  1. Draw a line connecting the two points (A&B).
  1. Place the index of the protractor at the point where the drawn line crosses a vertical (north-south) grid line. The index of a protractor is the center of the protractor. There is a vertical and a horizontal line to enable you to align the protractor.
  1. Keeping the index at this point, align the 0 to 180 degree base line of the protractor on the vertical grid line. When using the protractor, the base line is always oriented parallel to a north-south grid line. The 0 degree or 360 degree mark is toward the top of the north on the map and then the 90-degree mark is to the right.
  1. Read the value of the angle from the inner scale (outer scale is MILS and is used for other purposes, i.e. range cards); this is the grid azimuth from point A to point B.

PERFORMANCE STEP 9: Convert a grid azimuth to a magnetic azimuth

Examine your declination diagram.

Suppose that you plotted a 39-degree azimuth on your map, and you want to know what azimuth to follow on your compass. To convert that grid azimuth to a magnetic azimuth, you simply follow the instructions. By adding the G-M angle (e.g. 8 degrees) to the grid azimuth (39 degrees), you have converted the grid azimuth to the correct magnetic azimuth (47 degrees).

PERFORMANCE STEP 10: Convert a magnetic azimuth to a grid azimuth

Examine your declination diagram.

Suppose that you shot a 238-degree azimuth with your compass, and you want to plot this on your map. To convert that magnetic azimuth to a grid azimuth, you simply follow the instructions.  By subtracting the G-M angle (e.g. 8 degrees) from the magnetic angle (238 degrees), you have converted the magnetic azimuth to the correct grid azimuth (230 degrees).

 

Employ a map and compass

Evaluation Checklist

 

EVALUATOR(S):

MARINE TRAINED:

DATE:

SUPPORT REQUIREMENTS: Topographic map, protractor, map pens, and a lensatic compass

EVALUATOR NOTE: Marines must answer or perform all the questions below without error in order to pass this event. The evaluator will guide the Marine being tested through the checklist by asking questions.

Performance Step Instructor Notes Pass or Remediate
1.       Describe the marginal information found on a topographical map

 

Marine should identify and describe four of the following on a map:

1.     Sheet name

2.     Series name

3.     Scale

4.     Bar scale

5.     Contour interval

6.     Declination diagram

7.     Adjoining sheets diagram

8.     Legend

 

 
2.       Identify terrain features found on a topographical map

 

1. Marine should identify four of the following terrain features on a map:

1.     Hill

2.     Ridge

3.     Saddle

4.     Valley

5.     Depression

6.     Finger

7.     Draw

8.     Cliff

9.     Cut

10.  Fill

 

 
3.       Identify what colors represent on a topographical map

 

Marine should state the meaning of three of following colors on a map:

1.     Black: Manmade features

2.     Blue: Water features

3.     Green: Vegetation

4.     Red: Cultural features

5.     Brown: Terrain features

6.     Reddish-Brown: Cultural and terrain features

 

 

 
4.       Plot a point on a map using the protractor

 

Given a six-digit grid, the Marine should plot a point on a map.

 

 
5.       Determine the six-digit grid coordinate of a specific point on a map

 

Given a location on a map, the Marine should be able to determine the six-digit grid coordinate.  
6.       Determine the straight line and/or curved line distance between two points on a map

 

Given two points on a map, the Marine should be able to determine straight line or curved line distance between the points.  
7.       Determine a back azimuth

 

Given an azimuth, Marine should determine back azimuth.  
8.       Determine the grid azimuth between two points on a map

 

Given two points on a map, Marine should determine the grid azimuth between the two.  
9.       Convert a grid azimuth to a magnetic azimuth

 

Given a grid azimuth and a declination diagram, Marine should convert grid azimuth to a magnetic azimuth.  
10.   Convert a magnetic azimuth to a grid azimuth

 

Given a magnetic azimuth and a declination diagram, Marine should convert magnetic azimuth to a grid azimuth.  

 

 

Employ a Map and Compass

Training Support Package (TSP) for the Marine Battle Skills Test (BST)