INTRODUCTION TO THE MAP
101. A map is a scaled plan of a portion of the earth's surface.
As the earth's surface is curved, there is always some degree of
distortion on a map, due to the type of projection used. For example,
a large piece of orange peel, when flattened, will tear around the edges
and squash together at the centre. As long as the land area contained
on the map sheet is not large, this distortion will be small and will not
concern the map user.
105. It is not sufficient for a student of map reading to be able
to extract information shown on a map, give grid references, read and
plot bearings and measure distances. Mapcraft involves being able to relate
the map to the ground and the ground to the map. However much is known
about the technicalities of map reading, it will be largely wasted and
even dangerous without a mastery of mapcraft.
THE AIM OF MAP READING
107. The aim of map reading is to enable the adventurer to find
his or her way about the country and recognise features on
the ground and on the map and when necasary relate that to others
THE CARE OF MAPS
108. Maps are valuable documents They must be treated with
care to prevent damage. Most damage to maps occurs when the user
opens them out fully in the open air or in moving vehicles.
There is always a slight breeze to catch them and start tears which
quickly spread. To prevent tears, maps should be folded in such a way
that any part can be referred to without having to open the map fully out.
109. Figure 1 shows how to fold a map. It should be first folded
in half with the map details outwards. it is then folded across the
other way, concertina fashion, as illustrated. The number of folds
will depend on the size of the map. The aim is to reduce the map to
a convenient size for carrying and, at the same time, ensure that
there is a reasonably large area for studying when two folds are opened
like a book. Folded in this manner, any part of the map can be studied
by opening the appropriate folds.
110. Once a map is folded, it should be left folded. The details
at creases is bound to deteriorate but the deterioration will be less
than if the map was constantly folded and unfolded. The folded map
should be protected by placing it in a map case or plastic bag. The
map may also be protected by the use of a mapboard or stick-on clear
111. If the map has to be marked, it should be done lightly in pencil
so that the marks can be easily rubbed off. On operations, the marking
of maps must be avoided, as they may be of great value to the enemy if
they are captured.
MAP REFERENCE SYSTEMS
THE GRID REFERENCE SYSTEM
202. The grid consists of two sets of equally spaced parallel
lines intersecting at right angles to form squares. maps are
normally printed with North at the top of the sheet and with the
superimposed grid lines running vertically and horizontally.
The interval between grid lines is uniform throughout the map,
and is selected in accordance with the map scale. The intervals
shown on military maps are as follows:
1:25 000 to 1:100 000 &NBSP; 1 000m
1:250 000 to 1:500 000 &NBSP; 10 000m
1:1 000 000 &NBSP; 100 000m
203. When giving grid references, the grid lines are referred to as
a. Eastings - the vertical grid lines, which divide the map
from west to east.
b. Northings - the horizontal grid lines, which divide the
map from south to north.
GIVING GRID REFERENCES
204. When giving grid references, the easting (ie. the left to right
reading of grid values) is always given before the northing (ie. the
bottom to top reading of grid values).
FOUR FIGURE GRID REFERENCE
205. Four figure grid references indicate the position of
one grid square only and are useful when identifying major
features and localities. To indicate a particular grid square,
the easting, which forms the left or western boundary of that
square, is selected first. Next, the northing, which forms the
southern or bottom boundary of the square, is selected. The two
figures for the easting and the two figures for the northing,
combined in that order give the four figure reference required.
206. A four figure grid reference to Square A in Map 11 is given
according to the following sequence:
a. select the easting which forms the west boundary of
Square A. In this case it is easting 60
b. select the northing which forms the south boundary
of Square A. In this case it is northing 60
c. therefore, the four figure grid reference to Square
A is GR6090.
SIX FIGURE GRID REFERENCE
207. Six figure grid references are used to indicate positions
to within 100 m accuracy. To give a particular grid reference,
imaging that each side of the square is divided into 10 equal
parts and that the whole grid is divided into 100 smaller squares.
Estimate which small square the particular object is in.
In Map 12, the numbering of the lines forming the small squares
indicate the number of tenths of a unit there are east of easting
71 or northing 13. The house A is in the small square 71.7 and
northing 13.7. Deleting the decimal points, the six figure grid
reference to house A is 717137. Grid references are always prefixed
with the letters GR to avoid confusion.
EIGHT FIGURE GRID REFERENCE
208. Eight figure grid references can normally only be given
on maps with a scale of 1:50 000 or larger. The method is
similar to the six figure method explained in paragraph 207,
except that each small square is again divided into 100 still
smaller squares to give an accuracy to within 10 m. The result
is that the eastings are then calculated to four figures and
the northings to four, the combination being and eight figure
grid reference. For example, in Map 12, house A is at GR 71761371.
MAP SCALE & MEASURING DISTANCE
301. As a map is a scaled plan, the relationship of the
horizontal distance between two points on the ground, and
the distance between the same two points on a map, is constant,
regardless of the direction or location of the distances measured.
The determination of distance is an important factor in the
planning and execution of a military mission.
302. As discussed in chapter 1, maps are produced at various scales
for specific purposes. The scales are referred to as small, medium
or large, and are defined as follows:
a. small scale is 1:600 000 and smaller
b. medium scale is larger than 1:600 000 but smaller
than 1:75 000
c. large scale is 1:75 000 and larger
EFFECTS OF CHANGE OF SCALE
303. As discussed in section 6, a map's reliability cannot be
judged by the scale. Large scale maps show more detail.
A convoy commander, however, could find himself unnecessarily
cluttered with maps should he have to travel a considerable
distance using large scale maps. When selecting a map, the
two main considerations are the amount of detail required and
the area covered. As a guide, choose the smallest available
scale that provides sufficient detail.
304. It is important to realise that halving the scale not
only halves the distance of identical points on the maps but,
as this occurs in all directions, the map area becomes quartered.
Maps of the same area, clearly show the loss of detail as the
scale becomes smaller.
METHODS OF EXPRESSING SCALE
305. The scale of a map is expressed as either:
a. a representative fraction (RF); or
b. a graphic scale
REPRESENTATIVE FRACTION (RF)
306. An RF expresses the distance on a map as a fraction
of the corresponding distance on the ground. If the scale
is 1:100 000, every distance on the map is 1:100 000th of
the distance on the ground. (eg 1cm on the map represents
1km on the ground). The numerator of the RF is always 1.
The larger the denominator of the RF, the smaller the scale.
307. The graphic scale shows how distances are represented on,
the map and assists in the measurement of distances.
On topographic survey maps, the scale is in kilometres
with secondary divisions in 100m. On JOG and smaller
scale maps, generally there are three graphic scales for
statute miles, kilometres and nautical miles. Care should
be taken to ensure that all measurements are taken from the
zero mark, which, on some maps, is in from the left of the scale.
MEASURING DISTANCES ON A MAP
308. There are many ways of measuring distances on a map, such
as using dividers, a length of string or the scale on a protractor
or ruler. This section explains the simple method of using the
straight edge of a piece of paper.
MEASURING STRAIGHT DISTANCE
309. To measure the ground distance in a straight line between
two points on a map, lay the straight edge of a piece of paper
against the two points and, at each point, mark the paper with
a tick. Then lay the paper along the graphic scale with the
left hand tick against the zero mark to determine the distance.
The distance A-B 3640m Map 16.
MEASURING CURVED LINE DISTANCE
310. To measure the distance along a curved line such as a
winding road, consider the road as a number of straight, or
nearly straight sections. As in Map 17, lay a piece of paper
along the first section and mark it at A and at the end of the
first straight section. Pivot the paper about the second mark
until it lies along the second section. Mark the end of the
second section and continue this method until B is reached.
The total distance by road is then recorded as a straight ling
on the piece of paper and can be read off against the linear
scale. The distance from A to B in Map 17 is 4900m.
RELIEF & CONTOURS
IMPORTANCE OF RELIEF
401. Man made features, such as towns, roads and
railways are incidents on the surface of the ground.
Their details change quite rapidly while the shape
of the ground, such as hills and valleys, changes
slowly. The relief of the ground has determined
the nature of life lived on it, the types of things
men build on it, the positions of towns and the direction
and forms of communications. Until relief can be read
from a map, it is only possible to learn very elementary
things about the country.
402. The importance of relief is obvious in navigation
and tactics. Relief affects the movement and deployment
of units by limiting the routes, along which they may travel,
their speed of movement, and the ease or difficulty of
attacking or defending an area. Also affected are
observation, fields of fire, cover, concealment and
the selection of key terrain features.
DESCRIPTION OF CONTOURS
403. Contour lines are lines on a map connecting points
of equal elevation. The vertical distance between adjacent
contour lines is known as the contour interval and is given
in the marginal information. Contour lines are printed
orange/brown on maps. Every fifth contour line may be
drawn with a heavier line to aid in measuring elevation.
These are known as index contour lines. Contours are
marked with their elevation at convenient places, with
their value read correctly when facing up the slope.
404. Contours not only gives representation of height
but also indicate the shape of the ground. This is best
illustrated by figure 9 which shows the perspective,
section and plan of a hill.
405. Each topographical form, such as a spur or
a knoll, produces its own particular contour pattern.
The most important things to remember about contour
patterns are as follows:
a. contours close together indicate steep slopes (figure 10)
b. contours far apart indicate gently slopes (figure 11)
c. when the spacing of contours, reading from high to low,
decreases, the slope is convex (figure 12)
d. when the spacing of contours, reading from high to low,
increases the slope is concave (figure 13)
406. It must be noted that, unless you know the direction
of the slope, each pattern might be its opposite. Thus, a spur
and a re-entrant have the same pattern (figure 14). When there
are no contour heights marked close by, and there is no feature
such as a river to show the direction of slope, always follow the
contours to the same point where their height is marked so that
you can tell which way the ground falls.
LIMITATIONS OF CONTOURS
407. The features that can be shown by contours are limited by
the vertical interval. If the vertical interval is 20m, features
of less prominence than 20m may not appear on the map.
Such features may be of tactical importance, particularly
in relatively flat ground. By practice on the ground, a student
can learn just how much he can expect the contours on a map to
show. It must be remembered that a map can never completely
substitute for a reconnaissance.
OTHER METHODS OF SHOWING RELIEF
408. Hachuring is a method of showing hill features by shading
in short lines drawn in the direction of the slope. These lines
show rising ground by shading up the line of slope, the shading
becoming heavier as the ground rises. Hachuring gives a good
impression of the shape of the ground as hills and valleys stand
out clearly. It has several disadvantages:
a. hachuring gives no exact information about height.
Therefore, heights and slopes cannot be
b. hachuring tends to obscure other detail on the map; and
c. hachuring varies with the type of country
(eg, in flat country, quite small features have to be
given a prominence equal to that of much larger features in hilly country).
409. Hill shading shows by colouring what hachures show in line.
The shading is applied so that depth of tint indicates the steepness
of the slope, the general tint becoming deeper as the ground rises.
Hill shading obscures detail less than hachures, but otherwise has
the same disadvantages.
410. A second method of hill shading depicts the shadows that would
be cast by high ground if light was shining from a certain direction.
This method can also be used in conjunction with contour lines.
411. Spot elevations are points on the map with the height of the
particular feature shown alongside. This gives accurate information
when used in conjunction with contours. Other types of spot elevations
are horizontal control points, trig points and bench marks.
412. Layer tints are used in conjunction with contours. The space
between the contours is coloured with tints that vary according to
height above sea level, the colours becoming deeper as the height
increases. Each tint may cover the vertical interval of several
contours. This makes the high ground obvious at a glance.
413. Form lines are approximate contours that have not been
accurately surveyed in. They show the shape of the ground in a
similar manner, but cannot be relied upon for accurate information
about heights, slopes and visibility.
414. The study of landforms from an examination of the contour
lines is adequate for many purposes but, when precision is demanded,
a section is usually required. A section is an exaggerated side view
of a portion of the earth's surface along a line between two points.
415. A section can be constructed from any contour maps as shown
in figure 15. The construction of a section requires the following steps:
a. Draw a line (section line) on the map between the
two points between which a section is desired.
b. Find the value of the highest and lowest contour lines
that cross or tough this section line. Add one contour
value above the highest and one below the lowest to take care of hills
c. On a blank sheet of paper, draw enough equally spaced
horizontal lines so that there will be one line representing
each contour value, as determined in sub-paragraph b.
d. Place the lined paper on the map with the lines adjacent
and parallel to the section line.
e. Number the line on the lined paper, with the highest
value determined in sub-paragraph b closest to the section line.
f. Number the rest of the lines in sequence down to
the lowest value on the line farthest from the he
g. From every point on the section line where a contour
line crosses or touches, drop a perpendicular
to the line having the same value as the contour. Place a tick mark
where the perpendicular line crosses the line.
h. The highest point of hills and the lowest point of
valleys will have to be determined by estimation
and then a perpendicular dropped to their estimated value.
i. After all perpendiculars have been dropped to the
lined paper, connect all tick marks with a smooth,
natural curve. Remember that hills and valleys are usually rounded.
Streams, however, tend to form a sharp
V-shape or a U-shape.
j. The section just drawn may be exaggerated.
The spacing between the lines drawn in sub- paragraph
c will determine the amount of exaggeration and may be varied to
suit any purpose.
416. When time is short, or when a complete section is unnecessary,
a section may be constructed showing only the hill and ridge tops and,
if desired, the valleys. This is called a hasty section. It is
constructed in the same manner as a full section but only show the
417. The slope of the ground may be expressed as the angle the
ground makes with the horizontal, but more commonly as a gradient,
eg, 1 in 10 or 1 in 20, which may be written as 1:10 or 1:20.
A gradient of 1 in 10 means that in a distance of 10 units horizontally,
the ground rises or falls 1 unit.
418. Gradients may be measured on a map by comparing the
vertical distance (VD) to the horizontal distance (HD) for a
particular slope. VD is the difference between the highest and
lowest elevations of the slope and is determined from the he contour
lines. HD is measured between these highest and lowest elevations.
Both the vertical and horizontal distance must be expressed in the
419. Gradients can be expressed in the following ways:
a. a fraction
b. a percentage
c. a slope angle; is obtained by multiplying the
gradient by 57.3 to get an approximate answer in
degrees. This method is reasonably accurate for angles under 20
420. The eye exaggerates slopes to the extent that many people
looking down a slope of 1 in 1 would say that it was almost vertical.
Looking down a slope of 1 in 3 or 1 in 4, they would be convinced that
it was at least 1 in 1. Unless it is known what various gradients
look like on the ground, a wrong impression of the ground may be
obtained by studying a map. The ground will appear much flatter
than it really is. Figure 17 shows the effects of various gradients.
go now to the second part of navigation