Map reading and the ability to navigate is a fundamental skill essential to all Army soldiers throughout their entire careers. Historical studies on leadership reveal that a strong appreciation of terrain and its proper use is characteristic of all great combat leaders. Land navigation and map reading is a starting point to developing this essential task.
NOTE: A 1:50,000 scale map, protractor, compass,
pencil and paper would be useful aids in this lesson.
a. Before proceeding, you must first understand what a map is. A map is a graphic representation, drawn to scale, of a portion of the earth’s surface as seen from above.
(1) Manmade and natural features are depicted by symbols, lines, colors, and forms
(2) The ideal representation would be realized if every feature of the area being mapped could be shown in true shape and size. Obviously, this is impossible. These features must be represented by conventional signs and symbols. To be legible, many of these must be exaggerated in size.
b. A map could be compared to a piece of
equipment. The first thing you should
check on new equipment is the “instructions for use.” In the margin of the map, the map maker has provided
information. Before using any map, you
should first check the marginal information.
Unfold your map sheet. Graphic-3
(1) Sheet Name:
The sheet name is found in two places:
in the upper center margin and either the right or left side of the
lower margin. On this map you see the
word “Columbus.” This is the sheet
name. It was taken from the most
outstanding cultural or geographic feature within the mapped area.
(2) Sheet Number: the sheet number is also found in two places. Look at the upper right margin. You will find the word “sheet”, some
numbers, and a Roman numeral. This is
the sheet number. This sheet number can
also be found in the lower left margin.
This number identifies this map sheet from all other map sheets.
NOTE: Look down the right margin to the lower
right corner until you come to the statement “This map is red-light
readable.” This is a special note
containing information that relates to the specific map sheet on which it
appears. In this case, it tells us that
the map can be read under red-light conditions. Graphic-4
(3) Adjoining Sheets: Notice that the center box is labeled "Adjoining
sheets." This box has been further divided into smaller rectangles.
The center box is outlined in heavy black line, and it contains a number which
is the same as the map's sheet number. This is the index to adjoining sheets.
It tells you what map sheet you would need to navigate in an area adjacent to
the area covered by this map sheet.
(4) Declination Diagram: Move to the left and you will find the
declination diagram. It shows the
angular differences between true north, grid north, and magnetic north. This diagram will be discussed later during
the G M angle portion of this block of instruction.
(5) Scale:
In the bottom center margin you will see the word "Scale"
followed by numbers 1 :50,000 (one, colon, fifty thousand). This means that one unit of measurement on
the map is equal to fifty thousand of the same unit on the ground.
(6) Bar Scales: Directly beneath the map scale you will find the bar scales.
These are used to convert map distance to ground distance and vice versa.
(7) Contour Interval: Beneath the bar scales you will find the contour interval
note. This gives the vertical distance
between contour lines, and the unit of measurement which is usually either feet
or meters.
(8) Credit Note: Beneath the contour interval note you will see a nine-line paragraph. This is the credit note. It gives two important items of information. It tells you who made the map and when it was printed.
(9) Grid Reference Box: Below the credit note you will find a large
rectangular box. This is the grid reference box. In the grid reference box, the
grid zone designation, and the 100,000 meter square identification is found.
Notice the 100,000 meter square identification for this map is FL and LG.
You will be using this information later.
(10) Legend:
Move to the bottom left hand corner and notice that this area is covered
with colors and symbols. This the
legend. This is where the mapmaker tells the user what colors and symbols stand
for on this map. the symbols are not
always the same on every map.
Always refer to the legend to avoid errors when reading a map.
(11) Glossary:
There is no glossary on this map.
If this was a map of an area in a country whose native language was
other than English, there would be a glossary.
The glossary is a dictionary. It
lists nouns and their translation in the native language and in English.
c. The mapmaker uses colors and symbols to
represent natural and man-made features.
The 1:50,000 military map has five basic colors that show information
about natural and man-made features.
The use of colors will vary, depending on the date of the particular
map. These colors and what they
represent are:
(1) Black: Indicates cultural (man-made) features, such
as buildings and roads.
(2) Blue: Identifies hydrography or water features such as lakes, swamps,
rivers, and drainage.
(3) Brown: Identifies all relief features and
elevation, such as contour lines on older nonredlight readable maps
(4) Green: Identifies vegetation with military
significance, such as woods, orchards, and vineyards.
(5) Red: Classifies cultural features, such as populated areas, main
roads, and boundaries on older maps.
You also may see Red-Brown on the map sheet. The colors red-brown are combined to
identify cultural features, all relief features, and elevation, such as contour
lines on red-light readable maps.
Occasionally, other colors may be used to show special information. These are usually indicated in the marginal
information.
d. Here are examples of man-made objectives.
(1) Graphic-5
Difference between
an improved and unimproved road. (An
improved road has some type of drainage.)
(2) Graphic-6 Prominent fence. (The fence is constructed of any material that causes the fence to remain standing long enough for it to be as a navigational aid.)
NOTE: You cannot tell how many stories high the
building is because you are looking at it from above. The important thing to remember is that the symbol is not to
scale, but the center of mass of the symbol is placed on the map as close to
the exact location as possible.
(3) Graphic-7 Shown on this slide are symbols for a stream, an intermittent stream, a lake, or pond. An intermittent stream, lake, or pond contains water only after heavy rainfall. However, this water may remain for several days.
(4) Graphic-8
Here are several symbols for the types of vegetation: marsh, grassland, wooded area, and vineyard
or orchard. Notice that the symbol for
a marsh is blue, yet grass appears in it.
The grass is shown as blue because the water in the swamp is of greater
military significance than the vegetation.
You will notice that the objects in the vineyard or orchard symbol are
located symmetrically. This is because
crops are usually planted in a symmetrical manner.
QUESTION: HOW ARE
MANMADE AND NATURAL FEATURES DEPICTED
ON A MAP? ANSWER: BY SYMBOLS, LINES, COLORS, AND FORMS.
QUESTION: WHAT ARE
THE FIVE BASIC COLORS FOUND ON A MAY? ANSWER: BLACK, BLUE, BROWN, GREEN, AND RED.
a. All terrain
features are derived from a complex landmass known as a mountain or
ridgeline. The term ridgeline is not
interchangeable with the term ridge. A
ridgeline is a line of high ground, usually with changes in elevation along its
top and low ground on all sides, from which a total of 10 natural or man-made
terrain features are classified.
(1) Graphic-9
This slide illustrates the relationship between a particular piece of
terrain and how it is represented on a map.
b. Major terrain features
(1) Graphic-10
Hill- a point or small area of high ground from which the ground slopes
down in all directions; contour lines forming concentric circles. The inside of the smallest closed circle is
the hilltop
(2) Graphic-11
Saddle- a dip/low point along a
ridge crest; either lower ground between two hilltops or a break in the level
crest. A saddle is not necessary the
lower ground between two hilltops; it may be simply a dip or break along a
level ridge crest. If you are in a
saddle, there is higher ground in two opposite directions and lower ground in
the other two directions. A saddle is
normally represented as an hourglass or by figure eight shaped contour lines
.
(3) Graphic-12
Valley- reasonably level ground bordered on the sides by higher
ground. Generally has maneuver room and
might contain a stream. Contour lines
form a U. Lines tend to parallel stream
before crossing. Contour line crossing
a stream always points upstream.
(4) Graphic-13
Ridge- a line of high ground with height variations along its crest;
contour lines forming a U or V with the closed end pointing away from high
ground.
(5) Graphic-14
Depression- low point or hole in
the ground with higher ground on all sides.
Closed contour lines that have tick marks pointing toward low
ground. Usually only depressions that
are equal to or greater than the contour interval will be shown.
c. Minor terrain features
(1) Graphic-15
Draw- like a valley but normally
has less developed stream course than a valley. No level ground and little or no maneuver room. Ground slopes upward on the sides and toward
the head of the draw. Contour lines are
V- shaped with the point of the V toward the head of the draw (high ground).
(2) Graphic-16
Spur- short, continuously
sloping line of higher ground jutting out the side of a ridge. Often formed by two roughly parallel streams
cutting draws down a ridge. Contour
lines depict a spur with the U or V pointing away from high ground.
d. Supplementary terrain features
(1) Graphic-17
Cliff- a vertical or
near-vertical slope; it is an abrupt change of the land. . A cliff may be shown on a map by contour
lines being close together or touching, or by a ticked carrying contour line. The tick always points toward lower ground.
(2) Graphic-18
Cut- a cut is a man-made
feature, such as when a hill is cut away to lay a level bed for a road or
railroad track. It is shown on a map
when it is a least 10 feet high. The
contour line extends along the length of the cut. The tick marks point toward the roadbed.
(3) Graphic-18
Fill- a fill is where a low area
has been filled-in to level off a place, such as for a railroad track bed. The contour lines extend along the fill
area. The tick marks point toward lower
ground.
QUESTION: WHAT ARE
THE FIVE MAJOR TERRAIN FEATURES FOUND ON A MAP? ANSWER: HILL, SADDLE,
VALLEY, RIDGE. AND DEPRESSION.
QUESTION: WHAT ARE
THE TWO MINOR TERRAIN FEATURES FOUND ON A MAP? ANSWER: DRAW AND SPUR.
QUESTION: WHAT ARE
THE THREE SUPPLEMENTARY TERRAIN FEATURES FOUND ON A MAP? ANSWER:
CLIFF, CUT AND FILL.
a. We have been
discussing colors and symbols used by
the map maker. Now let's discuss
how we can locate these symbols on a map.
b. The system is the Military Grid Reference
System. The military grid reference
system is based on the Universal Traverse Mercator Grid or the UTM Grid. An understanding of the UTM grid will aid
you in using the military grid reference system.
c. Shown here is the UTM Grid System. It goes from 80 degrees south latitude to 84
degrees north latitude and is divided into a series of grid zones. These grid
zones are numbered from one to 60 around the world. Each zone is further divided into grid zone segments. Each segment is identified by a single
letter, starting with "C" and going through "X" The letters
"I" and "O" have been omitted to avoid confusion with the
numbers one and zero.
d. If a mercator projection of the world is
placed on this grid system, this is how it would look. Let's say we are located in the 16S grid
zone segment, which is the darkened square.
If this segment is enlarged, we can then see how the military grid
reference system comes into effect.
e. The map maker has further divided these
segment into 100,000 meter squares. Each of these 100,000 meter squares is
identified by two letters of the alphabet.
Here we see the 100,000 meter squares "FL" and
"GL." These squares have been
further divided by series of north south and east west grid lines.
f. Here you see the Columbus map sheet. Notice that it covers only a small portion
of the FL and GL squares. You might still be having difficulty seeing
the north south and east west grid lines, so let's enlarge a
portion of the Columbus map sheet.
Graphics -21 & 21A.
g. This is a section of the Columbus map sheet.
You should be able to clearly see the north and south and east and west
grid lines. Notice that where the lines
cross they form squares. Each side of these squares are 1,000 meters. Notice that the numbers increase to the
right and up. This is the cardinal rule
of map reading. Always read a map right
and up. Specific locations on a map
can be referenced by grid coordinates which identify the grid square and the
relative position of the point within the grid square.
h. Suppose you wish to reference Spot Elevation
445. To locate this point to within
1,000, meters you simply locate the grid square in which the point lies. To do this, start at the left of the map
sheet and read right to the north south gridline that immediately
precedes the point. In this case it is north south grid line 04. Then read up from the bottom of the map
sheet to the east west grid line that immediately precedes the point. In
this case it is east west grid line 91.
The value of the two grid lines gives you 4 digit coordinate which
locates the point to within 1,000 meters.
NOTE: Write 0491
--- 1,000 M on Graphic-26
i. You can locate this point even closer than
1,000 meters. You can locate it within
100 meters using interpolation.
Interpolation is a method in which you mentally divide the sides of the
grid square into ten equal segments of 100 meters each. Looking at spot elevation, 445 you can see
that it lies approximately two-tenths of the way or 200 meters to the right
into the grid square. This gives you a right reading of 042. Reading up you can see that the point lies
approximately nine-tenths of the way or 900 meters up into the grid square
giving you an up reading of 919. You
now have six digit coordinates which locate the point to within 100
meters.
NOTE: Write 042919 100M on Graphic-26. Use
Graphics 22, 24 & 25 to work additional problems, if necessary.
Graphic can also
demonstrate reading coordinates on map edges.
j. Unless your eyes are much better than mine,
you will not be able to locate the point to within any closer than 100 meters
without an instrument to aid you. The
instrument that you will use is the coordinate scale.
k. On the coordinate scale there are three
scales; the 1:25,000 /1:250,000 scale, the 1:50,000 scale and the
1:100/000. First, let's look at the
1:25,000 scale.
Notice that it has two sides, a vertical and a horizontal
side. These sides are 1,000 meters in
length. The point at which the sides
meet is the zero zero point. Each
side is divided into ten equal 100 meter segments by long tick marks and
numbers. These 100 meter segments are simply dividing the 20‑meter
segments into ten meter segments, you can locate a point to within ten
meters. On the 1 :50,000 scale there
are also two sides, a vertical side and a horizontal side. These sides are 1,000 meters in length. The point at which the sides meet is the
zero zero point. Each side is
divided into ten equal 100 meter segments by long tick marks and
numbers. These 100 meter segments
are subdivided into 50 meter segments by short tick marks. Again, by using interpolation, you can
locate the point to within ten meters.
l. To use the
coordinate scale to locate a point the first thing you must do is look in the
marginal information of the map and determine the scale of the map you are
using. Then using the appropriate
scale, place the zero zero point in the lower left hand corner of the
grid square in which the point is located.
m. Now, slide the scale to the right keeping
the horizontal scale directly over the east west grid line the vertical
scale cuts center of mass of the point. Reading right you can see that the
point lies 200 meters to the right into the grid square, giving you a right
reading of 0420, and reading up the
point lies meters 910 meters up into the grid square, giving you up reading of
9191. Written as coordinates it looks
like this.
NOTE: Write on graphic: Grid coordinate 04209191 10M.
n. If you only wanted a six-digit grid, you
would use the 100-meter mark that was nearest the point. By using these eight digit coordinates
you have located Spot Elevation to within ten meters. Notice that I have written my coordinates as a continuous series
of even digits with no punctuation of any kind. This is the way you should write
your coordinates.
NOTE: Make sure coordinates are neatly written to illustrate reading right and up.
Example:
0491-------- 4 Digit Grid 1000 M
042919----- 6 Digit Grid 100 M
04209191---8 Digit Grid 10 M
o. Could the coordinate 04209191 be located on
any other map sheet? Yes. It is possible that these coordinates could
locate a point in any one of the 100,000 meter squares. Therefore, it is important that you prefix
your coordinates with the proper 100,000 meter square identification letters
that are shown in the grid reference box.
The coordinate is on the map sheet.
Take out your map sheet and tell me which 100,000 meter square
identification letters I should use to prefix these coordinates.
QUESTION: WHICH
100,000 METER SQUARE IDENTIFICATION SHOULD BE USED? ANSWER: GL (Be prepared
to explain.)
QUESTION: A SIX
DIGIT GRID COORDINATES WILL LOCATE A POINT TO WITHIN HOW MANY METERS? ANSWER: 100 METERS.
QUESTION: AN EIGHT
DIGIT GRID COORDINATES WILL LOCATE A POINT TO WITHIN HOW MANY METERS? ANSWER: 10 METERS
NOTE: Practice determining 8 digit grid
coordinates.
a. You have seen how
you can use grid coordinates to locate a specific point on the map. If you can locate one point, you can locate
two, and the next logical question that comes to mind is how far is it from one
point to the next.
b. In order to convert ground distance to map
distance, or vice versa, on the map you will need an aid. The map maker has given you this aid in the
bar scales located in the margin of the map.
c. Here you see the three bar scales that you
will generally find on a map: kilometers, statute miles, and nautical
miles. In order to measure distance
correctly, there are two things you must remember.
(1) First, use the appropriate scale. If you want a distance measurement in
meters, make sure that you are using the metric bar scale.
(2) Second, notice that the zero or starting
point of the scale, is located within the scale and not at the end. This divides the scale into two parts. From
zero to the right is the primary scale,
divided into standard units of measurements.
From the zero to the left is the extension scale and is divided into
tenths of miles and hundreds of meters.
d. In military map reading, we are concerned
with two types of distance. Straight line
distance, and road distance. You would use road distance
when planning convoys and road marches.
e. Straight line distance can be
obtained from a military map by one of two methods.
(1). Use a straight edge of a sheet of
paper. Lay the straight edge on the map
between point A and B. Mark the paper
at both locations. Transfer the paper
to the bar scales and read the distance.
Place the first tick mark at the end of the scale, then slide the
straightedge to the left until the first tick mark lines up with the zero point
on the scale. Because there is 2,000
plus meters, continue to slide the straightedge into the extension scale,
stopping when the second tick mark lines up with the 2,000 meter point. Now the straight line distance is 2,000 plus
100, 200, 300, 400, 500, 600, 700 meters.
When measuring distance, measure to the nearest 10 meters or one tenth
of a mile.
(2). Use the scale found on the lensatic
compass. This scale is meant for
1:25,000 maps. Since we are using the
1:50,000 map, double the reading obtained from this scale.
f. To determine over a course that is not
straight such as a road, use one edge of the road or trail. Divide it into segments that are fairly
straight. Use the straight edge of a
sheet of paper and carefully transfer the tick marks at each end. Add each segment to the ones before it.
Transfer the paper to the bar scales and measure from the first to the last
tick mark. When actually traveling,
use the side of the road or trail that you measured and do not cross over, if
possible.
QUESTION: WHEN DETERMINING DISTANCE ON A MILITARY MAP WHAT TWO TYPES OF DISTANCE SHOULD YOU BE CONCERNED WITH?
ANSWER: STRAIGHT-LINE AND ROAD DISTANCE.
QUESTION: WHEN
WOULD YOU USE ROAD DISTANCE? ANSWER:
WHEN PLANNING CONVOYS AND ROAD MARCHES.
NOTE: Practice determining both straight line and road distance.
a. Being able to
determine distance between two points would be of little value unless you
consider direction also. When you look
at a map you can probably tell the cardinal directions of North, South, East,
and West. This is not always accurate
enough for our use. We must be more
specific. No matter where you are
located on the face of the earth, you can think of yourself as being in the
center of an imaginary circle. This
circle is divided into 360 degrees. In
the Army direction is given by using degrees.
Instead of the word DIRECTION, however, the word AZIMUTH is used. An azimuth is defined as a horizontal angle
measured clockwise from a base direction.
This base direction is always NORTH.
b. A moment ago I mentioned an imaginary
circle. The slide appears vertical but
imagine that it is horizontal, or the way the map sheet would be if you laid it
on the table. Notice that the base
direction of North has a value of either zero (0) or three hundred and sixty (360) degrees. If you wanted to move from your position at
Point "U" to Point "A," you would follow an azimuth of
forty-five degrees. To determine
the azimuth you must follow, draw a line connecting the two points, then read
around the azimuth circle from the base direction of north in a clockwise
manner to the point where the line cuts the azimuth circle.
QUESTION: If you
wanted to move from point "U" to point "B," what azimuth would you follow?
One hundred and twenty (120) degrees. Merely extend line "UB" until it
cuts the azimuth circle.
QUESTION: Keeping this in mind, what azimuth would you
follow from point "U" to point "C?"
c. One hundred and twenty (120) degrees. You can see that line "UB" is much
shorter than line "UC," yet you follow the same azimuth. This gives you an important rule about
azimuths. That is the distance has no
effect on an azimuth.
QUESTION: Keeping in mind that from "U" to
"A" is 45 degrees, what would the azimuth be from "U" to
"F?"
d. Two hundred and twenty-five (225)
degrees. We obtain this answer by using
a method called "Back Azimuth."
There is a simple rule for determining a back azimuth. The rule is: If the initial azimuth is less than one hundred and eighty (180)
degrees, ADD 180 degrees. If the
initial azimuth is more than one hundred and eighty (180) degrees, SUBTRACT 180
degrees.
e. Now unless your eyes are a lot better than
mine, you will not be able to merely look at a map and determine an
azimuth. You will need an aid. The instrument that is used is called the
protractor.
Graphics -29 & 30.
f. This protractor is square; however, it measures 360 degrees, the full value of the azimuth circle. On the scale, each tick mark equals one degree. When using the protractor, your base direction is still North. The starting point for measuring an azimuth with this instrument is the center cross or index. When measuring or plotting azimuths with the protractor, the base line should be parallel to a North‑South grid line, and the center cross should be at the center of mass of the point from which you are plotting, with 0 degrees at the top and 90 degrees at the right.
g. Imagine you are located here on the island
in the road junction in GL 0390 and you
must move to the road junction in 0591.
You can determine the azimuth between the two points by connecting the
two points with a straight line. Make sure the line cuts center of mass of both
points.
h. Place the index of the protractor at center of mass of point from which you are measuring with 0 degrees to the top and 90 degrees to the right, and the base line parallel to the North-South grid line. Start from the base direction of north and read in a clockwise direction around the scale until you come to the point where the line cuts the scale. Read the azimuth to the nearest 1 degree. In this case, the azimuth is 50 degrees.
i. You know that distance has no effect on
azimuth. Keeping this in mind, you can
move your protractor to a point where the line you have drawn crosses a North-South
grid line. Place the index of the
protractor at this point with the base line exactly over a North-South
grid line and again read clockwise around the scale to a point where the line cuts the scale. Now I see the azimuth is 51 degrees. Evidently the base line of my protractor was
not initially parallel. This technique
can be used to check azimuths.
j. To plot an azimuth from a known point, place
the index of the protractor at center of mass of the point with 0 degrees to
the top and 90 degrees to the right.
Align the base line of the protractor parallel with a N-S grid
line. A method of doing this is to count the number of tick marks from the base
line to a N-S grid line. By
ensuring that you have the same number of tick marks at both the top and bottom
of your scale, your protractor will be properly aligned and the base line will
be parallel to the North-South grid line.
k. Begin at the base direction of North and
read clockwise around the scale until you come to your desired azimuth. At this point make a tick mark on the
map. Connect the starting point and the
tick mark with a straight line and extend this line. Without moving from your location you can make a map
reconnaissance of the terrain over which you will be moving.
QUESTION: HOW DO YOU
DETERMINE A BACK AZIMUTH? ANSWER:
IF THE AZIMUTH IS LESS
THAN 180 DEGREES: ADD 180 DEGREES---IF
MORE THAN 180 DEGREES SUBTRACT 180 DEGREES
QUESTION: HOW
SHOULD THE BASE LINE OF THE PROTRACTOR BE ALIGNED WHEN PLOTTING AZIMUTHS. ANSWER:
PARALLEL TO THE NORTH-SOUTH GRID LINES.
a. By now you should
have an understanding of how to measure and plot azimuths. You learned that an azimuth is defined as a
horizontal angle measured clockwise from a base direction and the base
direction is always NORTH. However, there are three base directions of
north. They are: Grid North, True
North, and Magnetic North. To discuss the base directions of north, we need a
picture of the world.
b. The first direction of north is grid
north. When you measure grid azimuths
on a map with a protractor, you are using this base direction. The base direction of grid north is shown by
the NORTH-SOUTH grid lines on the map.
I’ve placed a map sheet on the world, drawn in the NORTH-SOUTH grid
lines, extended one, and labeled it GN for grid north.
c. The second base direction is true north
which is the direction from your location to the north pole. True north is shown on the map in the
declination diagram by a straight line, terminating in a star. To measure from this base direction, you
need a gyrocompass. Since you will not
be able to measure azimuths from this base direction, I will eliminate it from
our discussion at this time.
d. The third direction is magnetic north. A lensatic compass is used to measure azimuths
from the base direction of magnetic north.
The north-seeking arrow of the lensatic compass is attracted to the
terminus of the earth’s magnetic field, located near the Prince of Wales Island
in northern Canada.
(1) Magnetic north is shown in the declination
diagram of a map by a straight line, terminating in a half arrowhead.
(2) Where you are on the earth’s surface determines if you have an easterly or westerly declination.
e. Here, you see the two base directions that
you must understand: grid north when
using the map; magnetic north when using the lensatic compass in the
field. What is important, however is
the angular difference between them.
This angular difference is called the grid-magnetic or G-M angle.
(1) The G-M angle is always measured from the
base direction of grid north and has two elements. First, it has a direction.
This direction is either east or west depending which direction magnetic
north is located from grid north.
Second, the G-M angle has a value.
The value of the G-M angle is found in the declination diagram of the
map.
(2) Now, let’s see how this G-M angle affects
us. Imagine that you are located in the
area covered by this map sheet. you are
in a defensive position and have placed your observation post (OP) here.
NOTE: Draw an OP on Graphic-34. The OP is at intersection of GN and G-M
lines.
(3) The observer sees an enemy crew-served
weapon going into position at an estimated range of 1,000 meters. Taking out his compass, the observer determines the magnetic azimuth
to be 90 degrees.
(4) The observer reports this information to
the company command post (CP). The
individual in operations knows that this information should be plotted on the
map. He picks up his protractor, places
the index down at center of mass of the OP and, from the base direction of grid
north, he plots 90 degrees. He measures
1,000 meters and plots this point on the map.
Rounds fired by the artillery will not hit the target (point out on
Graphic.)
Graphics-34, 34A, &
34B
(5) The individual in operations should have
taken into consideration the value of the G-M angle and instead of plotting an
azimuth of 90 degrees, he should have plotted on an azimuth of 100 degrees from
grid north. when the fire mission is
fired, the target would receive hits.
the G-M angle must be always be considered when applying a magnetic azimuth
to the map or a grid azimuth to the lensatic compass.
(6) To find out whether to ADD or SUBTRACT the
value of the G-M angle when converting azimuths, a G-M angle diagram should be
drawn. The first step in the
construction of a G-M angle diagram is to draw in a vertical line and label it
grid north (GN).
NOTE: Use easterly G-M angle.
(7) Next, draw in a line to represent magnetic
north. This line will be east or to the
right of the grid north line.
Note: Show “any azimuth line”.
(8) Give the G-M angle a value. This comes from the declination diagram on
the map sheet you are using. For the
purpose of this example, we will assign it a value of 10 degrees. Next, draw a line from the base of the G-M
angle out to the right. This is the
“any azimuth line” and it represents any azimuth, magnetic, or grid from 0 to
360 degrees.
(9) Draw an arc from the closest base direction
of north to the “any azimuth line” and label it “m.” this represents any magnetic azimuth. Then, draw an arc from the remaining base direction of north (GN)
to the “any azimuth line” and label it “G”.
(10) Use this diagram to convert azimuths.
Note: Show and explain western G-M angle. Graphics 36, 36A, AND
36B.
QUESTION: WHAT ARE THE THREE BASE DIRECTIONS OF NORTH?
ANSWER: GRID NORTH,
TRUE NORTH, AND MAGNETIC NORTH.
QUESTION: WHEN WOULD
YOU USE GRID NORTH? ANSWER:
WHEN USING A MAP.
QUESTION: WHERE ON
THE MAP WOULD YOU FIND THE VALUE OF THE G-M ANGLE? ANSWER: THE DECLINATION
DIAGRAM.
NOTE: Practice converting azimuths.
a. So far we have
discussed the basic skills necessary to read a map. Now we will apply this knowledge to determine unknown
locations. Intersection is a method of
locating an unknown point by using azimuths from two known points.
b. Suppose we have two OPs located in front of
our defensive position. Both OPs can
see enemy activity. From OP1, the enemy
activity is 32-degrees magnetic and from OP2, it is 322 degrees magnetic. The G-M angle is 18-degrees easterly.
c. The magnetic azimuth from OP1 is 32
degrees. Convert this to a grid azimuth
by adding the 18-degree G-M angle. The
grid azimuth would be 50 degrees. Using
the protractor, plot this azimuth on the map.
d. Convert the 322-degree magnetic azimuth to a grid azimuth. the grid azimuth is 340 degrees. Using the protractor, plot this azimuth. The enemy is located where the line cross. Intersection is used when a distance determination cannot be made.
QUESTION: IF YOU DETERMINE A MAGNETIC AZIMUTH TO AN UNKNOWN POINT TO BE 45 DEGREES AND YOU HAD AN EASTERLY G-M ANGLE OF 10 DEGREES; WHAT WOULD THE GRID AZIMUTH BE?
ANSWER: 55 DEGREES.
QUESTION: TO LOCATE
AN UNKNOWN POINT BY INTERSECTION; HOW
ANY KNOWN POINTS MUST YOU HAVE? ANSWER:
AT LEAST TWO.
NOTE: Practice
determining locations using the intersection method.
a. We have just
discussed how to locate an unknown point using intersection. However, there are times when you may have
to locate your own unknown location. There are two techniques that can be used: resection and modified resection.
b. To work a resection problem, we must be able
to identify two positions, both on the ground and on the map.
(1) Looking out from our position we can see a
bridge. We determine the magnetic
azimuth to its location to be 159 degrees.
(2) For the purpose of this problem, assume that
there is a 1-degree westerly G-M angle.
(3) To plot the azimuth on the map, you must
convert to a grid azimuth. With a 1
degree westerly G-M angle, convert from magnetic to grid by SUBTRACTING 1
degree from the magnetic azimuth. This
gives you a grid azimuth of 158 degrees.
(4) Next, we must convert this grid azimuth to a
BACK azimuth by ADDING 180 degrees and plot the back azimuth of 338 degrees
from the bridge. Your location is
somewhere along this line.
(5) From our
location, we can also see a larger road intersection. the road intersection is on a magnetic azimuth of 117
degrees. The grid azimuth is 116
degrees.
(6) Next,
the grid azimuth must be converted to a back azimuth. The back azimuth of 296 degrees is plotted
from the road intersection. Your
location is where the lines cross.
(7)
The rule to remember when determining
a back azimuth is: Degrees: Less than 180 degrees, add 180 degrees. More than 180 degrees, subtract 180
degrees. When using Mils: if it’s Less
than 3200 mils, add 3200 mils. More
than 3200 mils, subtract 3200 mils.
NOTE: Practice
determining locations using the resection method.
c. The other technique you can use is modified resection. To use this method, you must be physically located on a linear such as a road, stream, or canal. You must also be able to determine an azimuth from your unknown location to a known point and then use this azimuth to resect back to your unknown location.
(1) Assume that you are in an area with an 18
degree westerly G-M angle. You are located
somewhere along a road which you can locate on the map.
(2) From your location, you can see a water
tower. The magnetic azimuth from your
location to the water tower is 85 degrees.
you must convert your magnetic azimuth to a grid azimuth by SUBTRACTING
the G-M angle. This gives you a grid
azimuth of 77 degrees. Next, you must
convert to a back azimuth. This is
accomplished by ADDING 180 degrees to the grid azimuth. The back azimuth is 257 degrees. Plot this azimuth from the know point (water
tower) and where the line resects (crosses) the linear feature (road). This is your location.
a. Up to now you have been applying azimuths to the map which were given to you and determining azimuths between points on the map; however, there will be many times that you will have to determine an azimuth to a point on the ground. These azimuths may be used during movement on the ground or applied to your map.
b. In determining an
azimuth with a compass, there are two methods which can be used. These are the compass to cheek and the
centerhold method. In order to use
either method you must understand the compass.
(1) The floating dial is used to determine the
direction in which you are pointing your compass. The outer “black” ring of numbers and tickmarks is used finding
directions in mils while the “red” inner ring is used for direction in degrees.
(2) There are 360 degrees or 6400 mils in a
circle. These are marked on the
floating disk by a tick mark every 5 degrees or 20 mils. However, not every tick mark is
numbered. You will have to determine
the number for these lines using the numbers that are shown.
(3) To determine a direction, point the compass
in the direction you want to go or want to determine. Look beneath the index line on the outer glass cover and estimate
to the nearest 3 degrees or 10 mils the position of the index line over the red
or black scale. Be careful to hold the
compass still so that the dial remains stationary while you are reading the
scale. If you understand these readings
and can apply either of the holding and sighting techniques of shooting an
azimuth, you will be proficient in performing this task.
(4) As you can see, we have now added the index
line. where the index line crosses the
scales of the floating disk, it shows an azimuth of 312 degrees and 5500
mils. If you understand these readings
and can apply either of the holding and sighting techniques of shooting an
azimuth, you will be proficient in this task.
c. When an azimuth has to be accurate you must
use the compass-to-cheek method. To do
this, open the cover to a 90 degree angle to the base. Position the eyepiece at a 45 degree angle
to the base.
(1) Once you have the compass open, place your
thumb through the thumb loop, form a steady base with your third and fourth
fingers, and extend your index finger along the compass base. The compass will then rest firmly on the remaining
fingers.
(2) Place the hand holding the compass into the
palm of the other hand. Bring both
hands up to your face and position the thumb that is through the thumb loop
against the cheekbone.
(3) Look through the lens of the eyepiece. If the dial is not in focus, move the eyepiece up or down until the dial is in focus. Align the sighting slot of the eyepiece with the sighting wire in the cover on the point for which the azimuth is being determined. Look through the lens of the eyepiece and read the azimuth under the index line.
d. The second method for shooting an azimuth is
the centerhold method. This method is
only used when a precise azimuth is not required.
(1). To shoot an azimuth using this method, open
the compass so that the cover forms a straightedge with the base. The eyepiece is moved back out of the way
since it is not used.
(2) Next, place your thumb through the loop,
form a steady base with your third and fourth fingers, and extend your finger
along the side of the compass. Place the thumb of the other hand between the eyepiece and
lens, extend the index finger along the remaining side of the compass, wrap the
remaining fingers around the fingers of the other hand, and pull your elbows
firmly into your side. This will place
the compass between your chin and your belt.
(3) To measure an azimuth, turn your entire body
toward the object and point the compass cover directly at the object. Look down and read the azimuth from beneath
the fixed black index line.
(4) To lay out a direction to move on, hold the compass in the same manner. Rotate your whole body until the azimuth to be moved on is under the index line of the compass, then move in the direction of the cover.
QUESTION: WHAT ARE
THE TWO TECHNIQUES YOU CAN USE TO DETERMINE AZIMUTHS WITH A COMPASS? ANSWER: CENTERHOLD AND COMPASS-TO-CHECK METHODS.
QUESTION: WHAT IS
THE “RED” INNER RING ON THE COMPASS USED FOR?
NOTE: Practice determining a magnetic azimuth
using a lensatic compass.
a. In addition to
knowing the location of a point on the map and on the ground, you must be able
to determine the altitude of the point.
First lets discuss contour lines and contour intervals. The brown lines on the map are called
contour lines. Each line shows the
height above sea level. Contour lines
never cross one another. Printed at the
bottom of the map is the contour interval, which is the difference in height
(elevation) between one brown line and the one on either side of it. On the map with a scale of 1:50,000, the
contour interval is usually 20 meters.
This would make point A 80 meters higher or lower than point B.
(1) You can easily tell by the brown lines the
direction of uphill or downhill because every fifth line is heavier and has a
number that gives its elevation. Let’s
say that the contour interval is 20 meters.
Now you can tell that point A is 80 meters higher than point B. Also, if you know the ground distance
between points A and B, you can get an idea of the steepness of the slope.
(2) Widely spaced contour lines show a gentle
slope. When they are close together,
the slope is steep.
(3) When the contour lines are close together at
the top of a hill, the hilltop is pointed.
When the contour lines are widely spaced, the hilltop is flat.
b. In order to determine the elevation of a
point you must first, locate the point on the map (it must already be plotted
on the map or given as an eight digit coordinates.)
(1) Next,
Determine the contour interval of the map from the marginal information.
(2) Locate the index contour line nearest the
point for which the elevation is being sought.
(3) Count the number of contour lines, up or
down, that must be crossed to go from the numbered lines to the point and note
the direction to the point. If the
point is on a contour line, the elevation of the point is the same as that of
the contour line.
(a) For points less than
one-fourth the distance between contour lines, the elevation is considered to
be the same as the elevation of the nearest contour line.
(b) For points one-fourth to
three-fourths the distance from the lower line, add one-half the contour
interval to the lower line.
(4) To estimate the elevation of the top of an
unmarked hill, add half the contour interval to the elevation of the highest
contour around the hill.
(5) To estimate the elevation of the bottom of a
depression, subtract half the contour interval from the elevation of the lowest
contour around the depression.
(6) On maps that do not show elevation and relief
in as much detail as needed, supplementary contour lines may be used. Marginal information indicates how the lines
are used.
(7) Benchmarks and spot elevation also indicate
points of known elevation.
QUESTION: WHAT DO WIDELY SPACED CONTOUR LINES INDICATE?
ANSWER: A GENTLE SLOPE.
QUESTION: HOW DO YOU
ESTIMATE THE ELEVATION OF THE TOP OF A HILL?
ANSWER: ADD ONE-HALF THE CONTOUR INTERVAL TO THE HIGHEST CONTOUR LINE
AROUND THE HILL.
NOTE: Practice determining elevation.
a. In order to see a
piece of terrain with the same orientation as shown on the map, you must orient
the map. The most accurate way to do
this is by the use of a compass. With
the map level, place the compass parallel to a north-south grid line
with the cover side of the compass pointing towards the top of the map. This will place the black index line on the dial of the compass parallel to grid north. Since the needle on the compass points to magnetic north, we have a declination diagram on the face of the compass formed by the index line and the compass needle.
b. Rotate map and compass until the directions
of the declination diagram formed by the black index line and the compass
needle match the directions shown on the declination diagram printed on the
margin of the map. The map is then
oriented.
c. If the magnetic north arrow on the map is to the left of the grid north, the compass reading will equal the G-M angle (given the declination diagram). If the magnetic north is to the right of the grid north, the compass reading will equal 360 degrees (6400 mils) minus the G-M angle.
d. Remember to point the compass north arrow in
the same direction as the magnetic north arrow (2 above), and the compass
reading (equal to the G-M angle or the 360 degrees (6400 mils) minus G-M angle)
will be quite apparent. If the G-M
angle is less than 3 degrees (50 mils), do not line up the north arrow.
e. Some maps have a built-in protractor consisting of a pivot point “P” on the south neat line of the map and several degrees of arc along the north neat line of the map. The G-M line is obtained by connecting pivot point “P” with the appropriate value of the G-M angle (taken from the declination diagram) on the arc. The map may then be oriented by placing the compass parallel to this line and rotating the map and compass until the needle point is aligned with the continuous line formed by the index line and the sighting wire. The map is then oriented.
f.
You can also use the declination diagram to orient the map. First determine the direction of the
declination and its value from the declination diagram. 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.
g. 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.
h. 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 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.
i. Once the map is
oriented, magnetic azimuths can be determined with the compass. But the map should not be moved from its
oriented position; any change in its
position will move it out of line with magnetic north.
QUESTION: WHEN ORIENTING
THE MAP WITH A COMPASS AND MAGNETIC
NORTH IS TO THE RIGHT OF GRID NORTH, WHAT
SHOULD YOU DO? ANSWER: SUBTRACT THE G-M
ANGLE.
QUESTION: WHAT WOULD
DO IF THE G-M ANGLE IS LESS THAN 3 DEGREES?
ANSWER: YOU DO NOT HAVE TO LINE UP THE NORTH ARROW
a. You have just
learned how to orient a map using a compass.
Now we are going to learn how to orient a map to the ground by
map-terrain association. A map is
oriented when it is in a horizontal position with its north-south corresponding
to north-south on the ground.
b. Look at the map and the ground to find two
terrain features common to both, such
as hilltops, saddles, valleys, ridges, or depressions. By aligning the terrain features on the map
with the same terrain features on the ground, the map is oriented.
(1) Use man-made features. Man-made features could be an important
factor during terrain association. The
user must be familiar with the symbols shown in the legend representing those
features. The depiction of buildings,
roads, bridges, high- tension lines, and so forth, will make the terrain
inspection a lot easier; however, the age of the map must be considered, as
man-made features appear and disappear constantly.
(2) Use the hydrography. Inland bodies of water can help during
terrain association. the shape and size
of lakes in conjunction with the size and direction of flow of the rivers and
streams are valuable help.
(3) Match the terrain to the map by examining
terrain features. By observing the
contour lines in detail, the five major landforms (hill, valley, ridge,
depression and saddle) should be determined.
This is a simple task in an area where the observer has ample view of
the terrain in all directions. One by
one, match the terrain features depicted on the map with the same features on
the ground. in restricted terrain, this
procedure becomes harder; however, constant checking of the map as you move is
the determining factor.
(4) Compare the vegetation depicted on the
map. When comparing the vegetation, a
topographic map should be used to make comparison of the clearings that appear
on the map with the ones on the ground.
The user must be familiar with the different symbols, such as vineyards,
plantations, orchards, and so forth, that appear on the legend. The age of the map is also an important
factor when comparing vegetation. Some
important vegetation features were likely to be different when the map was
made. Another important factor about
vegetation is that it can change overnight by natural accidents or by man
(forest fires, clearing of land for new developments, farming, and so forth).
b. Check orientations obtained by this method
to keep from orienting the map in the wrong direction (that is, 180 degrees
out). This reversal may be prevented by
aligning two or more features.
c. Determining your location by terrain
association. The key to success in
land navigation is to know your location at all times. With this basic knowledge, you can decide
what direction and what distance to travel.
(1) Most important of all is the initial
location of the user before starting any movement in the field. If movement takes place without establishing
the initial location, everything that is done in the field from there on is a
gamble. Determine the initial location
by referring to the last know position, by grid coordinates and terrain
association, or by locating and orienting your position on the map and on the
ground.
(2) You can also determine a location by using the intersection, resection, and modified resection techniques.
QUESTION: WHAT ARE
SOME OF THE WAYS YOU CAN ORIENT A MAP TO THE GROUND? ANSWER: USING MAN-MADE FEATURES, HYDROGRAPHY, COMPARE VEGETATION,
MATCHING TERRAIN FEATURES.
QUESTION: WHAT ARE
SOME OF THE TECHNIQUES YOU CAN USE TO DETERMINE YOUR LOCATION? ANSWER:
INTERSECTION, RESECTION, AND MODIFIED RESECTION.
a. Your platoon will
spend more time moving than fighting during combat. Therefore, make the best use of the terrain your unit will be
moving over.
(1) Because a moving unit usually contacts the
enemy at a time and place of the enemy’s choosing, you must use the terrain to
your best advantage. Proper use of the
terrain has two advantages:
(a) Cover and concealment to
protect the unit during movement.
(b) Maximum effectiveness of the
unit’s weapons.
(2) To properly use those advantages, you must
understand the military aspects of terrain and be able to apply them to any
given situation, whether it be defense, a delay, or a road march behind the
forward edge of the battle area (FEBA).
b. The primary requirement for any type of
movement on the battlefield is cover and concealment.
(1) Cover is any type of shielding from the
effect of weapons fire, especially direct fire. You must take advantage of every ravine or depression in the
ground to protect and cover your force, especially if you are forward of the
FEBA. You must evaluate the terrain,
the capabilities of the enemy’s weapon systems, and the position of known or
suspected enemy emplacements. Visualize
a cross section of the terrain and determine where the enemy cannot place
effective direct fire on your proposed route.
2) Concealment is
anything that hides or disguises your force.
You must consider concealment from both air and ground observation. If you are mechanized, exhaust smoke or dust
can reveal your unit to the enemy.
c.
If you are moving in an area where contact with the enemy is expected,
you must ensure that your proposed route can be covered by fire from your
overwatch or fire support positions.
Those positions must have good observation and fields of fire.
(1)
Direct fire weapons must have good observation to fire at known or
suspected enemy positions along your movement route. You must have observation to control the maneuver of your
elements if they make contact. Consider
the effects of smoke and dust from friendly and enemy fire.
(2) Select a route that gives your unit the best
fields of fire. Your machine guns and
antitank weapons must have good fields of fire to be effective. They must be in a position to provide
suppressive fires immediately. Using
your crew-served weapons to overwatch your movement, they must be able to
observe your route and fire in your support all the way to the objective. The overwatch positions that you select must
have unobstructed fields of fire to the next overwatch position.
(3) You must select the route that provides the
most favorable tactical advantage and meets the mission requirements. If enemy air is active or enemy ground
forces are in the area of the route, you must take maximum advantage of cover
and concealment. If speed of movement
is critical, the route should be over the most negotiable terrain, avoiding
difficult obstacles. The route should
include movement from one easily distinguishable terrain feature to
another. When ordered to move, you must
check the terrain based on the above considerations and select the quickest and
safest route.
(4) Planning a route can be aided by the use of
special-purpose maps and aerial photographs.
If those aids are available, use them to ensure you have the most
current information.
(5) Map reconnaissance, however, is no substitute for ground reconnaissance. If time is available and the tactical situation permits, reconnoiter the route you have to move over.