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GIFT OF




TRAINING MANUAL

IN

TOPOGRAPHY, MAP READING
AND RECONNAISSANCE



Prepared by

MAJOR GEORGE R. SPALDING

CORPS OF ENGINEERS
Under the direction of the Chief of Engineers, U. S. Army







WASHINGTON
GOVERNMENT PRINTING OFFICJ

1917



TRAINING MANUAL

IN

TOPOGRAPHY, MAP READING

AND RECONNAISSANCE



Prepared by

MAJOR GEORGE R. SPALDING

CORPS OF ENGINEERS
Under the direction of the Chief of Engineers, U. S. Army




WASHINGTON

GOVERNMENT PRINTING OFFICE
1917






ADDITIONAL COPIES

OF THIS PUBLICATION MAY BE PROCURED FROM

THE SUPERINTENDENT OF DOCUMENTS

GOVERNMENT PRINTING OFFICE

WASHINGTON, D. C.

AT

20 CENTS PER COPY



TRAINING MANUAL IN TOPOGRAPHY, MAP READING,
AND RECONNAISSANCE.



LESSON I.



TOPOGRAPHY.






1. So important is the influence of "the lay of the land" upon mili-
tary operations that every officer must thoroughly acquaint himself
at the earliest practicable moment with the topography of the area
within which his responsibilities lie.

2. A mere knowledge of the main roads, of the direction and dis-
tances to near-by towns is by no means sufficient. He must know
where the plains are, where the hills rise, how the streams run. He
must have a mental picture, a bird's-eye view, impressed on his brain
of the main physical and military features of his territory.



EROSION.



3. The faculty for grasping the topography of an area as a whole is
rarely a natural one. " To the beginner" in the study of topography
1 ' every JiiU is an isolated feature the elevations and depressions of
ground present to him nothing but irregularity and confusion."

4. As a matter of fact, there is a considerable degree of regularity
and system in our present-day ground forms. Whatever may have
been the irregularity and confusion of the original surface of the earth,
practically all of the ground forms which we Know to-day are the result
of erosion.

5. It has been estimated that the average elevation of the land
surface has been reduced 7,000 feet by erosion. Winds and waves,
glaciers, chemical action, frost, and plant growth have all had their
part in the breaking up and wearing down of the original rocks, but
by far the larger portion of the ground forms which exist to-day have
been carved out of the older formations by the action of running
water.

MASTER LINES OF TOPOGRAPHY.

6. Not all the water in heavy rains can seep into the soil; much of
it runs off. At one point a little stream begins; as it flows downward
another joins it; soon several unite into a fair-sized creek, which
rushes along carrying its burden of soil into the main valley, whence
the river may carry it on toward the sea. This simple process con-
tinued for ages has sufficed to carve out our deepest valleys. It is con-
tinuing to deepen them year by year, and more and more to wear
down the ridges between the valleys.

7. If our remaining ground forms are the result of such a process,
it is manifest that the drainage lines of an area, together with the
ridge lines, form a system of master lines which, once traced out and
studied, will give a grasp of the main features of the topography
that can be had in no other way.

3631C3



4 .TOPOGRAPHY, MAP BEADING, AND RECONNAISSANCE.

CONTOURS.

8. Tile main features of the topography, however, while of first
importance, are not sufficient for modern military operations. The
military leader must also know the relative sizes of the valleys, the
relative heights of the ridges, where the steep slopes are, where the
hills are flat. This information may be indicated upon a map in
several ways, but the best way is by a system of contour lines.

9. The beginner always has trouble with contours. He has learned
perhaps that a contour is a line connecting points of equal elevation ;
that contours do not cross; that a contour line either closes on itself
or both ends of it go off the map. But rules such as these, important
as they may be in checking up a sketcher's work, do not help the
beginner much. He is still hazy as to just what contours are and
how they represent ground forms.

10. It is true that a contour is a line joining points of equal eleva-
tion. But such a definition is not precise. A contour line is a line
each point of which has the same elevation. If one walks along a
contour line, he neither goes up nor down hill, but always on a level.
The surface of a quiet pond which has no outlet is practically level.
Therefore its shore line is a contour line. If one follows it hi the
direction of the hands of a clock he will find that he must turn to the
left at every entering valley, walk up the valley until he heads the water
line, cross the valley, then turn again to the right, following down the
other side of the vaUey to get around the point of the hill or spur which
lies between it and the next valley. His course will bend to the left
at every little inflowing drainage line, cross it, and turn again on the
other side to avoid leaving the level. We see then that vattey contours
apparently go in pairs, that is, there is always one of the same eleva-
tion on each side of the valley. They form a sort of a V which opens
out in the direction of water flow; point of the V upstream. Simi-
larly the spur contours apparently go in pairs. They form a sort of
U which opens out to the higher ground up the spur. (In glacial
country the valleys are more nearly U shaped and the ridges .sharp.)

11. The typical contour, then, is a curving line, alternately salient
and reentrant, a series of rude V's for the valleys and U's for the
spurs, the point of the V at the stream crossing, the curve of the U
at the ridge crossing. If the extreme points of the V 's and U 's are
determined and these points are connected by a curving line, opening
out gradually as we go downstream from the points of the V and
rounding out to the curve of the U, we get a line which will roughly
represent the contour of the ground for that elevation. In other
words, the points of the V 's, or the points where the contour crosses the
stream, and the points of the U 's, or the points where the contour crosses
the line of the watershed between two valleys, are essential control
points for the drawing of any contour line.

12. The single contour which marked the shore line of the pond will,
of course, give no indication of the shape of the hills which surround
the pond. To indicate these ground forms, we must have a number of
contours, each one of which shows the path which a man would fol-
low if he walked around the hill forms on a level line. These level
lines should be spaced at equal intervals in a vertical direction. In
other words, if we take the shore-line contour as the datum contour,
the next line should show the path which a man would follow if
walking on a level line, say, 10 feet higher than the pond, and the



TOPOGRAPHY, MAP BEADING, AND RECONNAISSANCE. 5

next, 20 feet higher, etc. This 10-foot vertical interval between the
level lines is called the contour interval or vertical interval. It may
be 1 foot, 5 feet, 10 feet", or 100 feet, or any other number of feet.

NOTE. Our Field Service Regulations provide that the contour interval should
be 10 feet for a military sketch made on a scale of 6 inches to the mile, 20 feet for a
sketch on a scale of 3 inches to the mile, and, in general, the proper contour interval
for any scale is to be found by dividing 60 by the number of inches on the scale which
represents a mile on the ground . This system of scales is known as the United States
Army; Normal System. The British Army have a similar system, using 50 as the
base instead of 60. In small-scale mapping these systems are usually not adhered
to. The United States Geological Survey use an interval of 20 feet for their 1/62500
(about an inch to the mile) sheets, reducing this to 10 or even 5 feet in very flat
country and increasing it for mountainous country.

CRITICAL POINTS.

13. It is manifestly impracticable in mapping to locate with
instruments in the field the points where each contour crosses each
drainage line, nor is this necessary. No map can show every change
of form of the ground. We must satisfy ourselves, therefore, with
locating the critical points of the master lines of the ground. Such
points are the heads, the changes in direction and the changes in slope
of the drainage lines; the tops, the changes in direction, and the changes
in slope of the ridge lines. It will also be impracticable to determine
the elevation of the head of every little gully or the location and
elevation of every change in direction of every drainage line or of every
ridge line. But we must locate the master critical points of the master
ridge and stream lines, and the elevation of these points must be
determined as well as the location of them. It is very important,
however, to plat in every gully, though the elevation of its head be
not determined, as these small drainage lines effect the shapes of
the hill forms very decidedly and, furthermore, they are landmarks of
great value. When the critical points an-d the drainage net has been
located as above described, one who knows something of the laws of
nature and remembers what a contour is can interpolate between the
master critical points enough of the others to enable him to draw in
all the contours.

INTERPOLATION.



14. Figure I is a skeleton sketch, giving the complete drainage net
and a few of the master critical points of a section of the Fort Leav-
enworth (Kans.) Military ^Reservation. The main stream line of
the area is shown as a solid line. The direction of flow is indicated
by the arrow near elevation 790 (upper right-hand corner). The
elevations of two points on the main stream are given (790 and 850).
Smaller tributary drainage lines are indicated in dashed line. Ele-
vations not on stream lines are critical points on the ridge lines.

15. .The problem is to draw logical contours at 10 feet vertical
intervals, with no other data than that given. The first step is to
locate the points where desired contours cross the mam stream line.
As there are no falls between elevation 790 and elevation 850, it is
assumed that the slope of the stream between these points is nearly
uniform, becoming, however, a little steeper as the stream is ascended.
Under this assumption the crossing points of contours 800, 810, 820,
830, and 840 are at once interpolated by eye on the main stream
between 790 and 850. By interpolation between these the eleav-



6



TOPOGRAPHY, MAP READING, AND RECONNAISSANCE.



tions of the points where each of the tributary ravines enter the
main stream are secured. Between these latter points and the heads
of the ravines, the elevations of which are given, the points where
the contours cross each of the ravines are marked.

16. Each point shown along the ridge lines was chosen as being a
critical point, that is, a point where the slope or direction of the riage
changes. From point to point along the ridge lines, it is assumed
that the slope is uniform. The points where the intervening contours
cross the ridge lines have, therefore, been interpolated. The result
of interpolation along stream and ridge lines is shown in Figure II.
As a rule the ridges and spurs of eroded hills point in the general




FIGURE I

direction of the junctions of the streams which have eroded them.
Therefore, interpolations have been made in these directions.

DRAWING THE CONTOURS.

17. In sketching in open country, where all the features can
be plainly seen, the method of drawing in the contours from
this control is to revisit the predetermined critical points and to draw
in all the contours which are needed to represent one feature, that is,
one spur or hill at a time, using the drainage lines as the limits of
the unit feature to be drawn. The smaller irregularities of the ground
are brought out by slight changes in contour spacing and contour
direction, here and there. (See Fig. III. ) Figure IV is the completed
sketch. It is very good representation of the ground.



TOPOGRAPHY, MAP READING, AND RECONNAISSANCE. 7/

PRACTICAL WORK.

18. At this point in his course, the beginner will be little benefited
by practice with sketching instruments, or by going out and merely
looking at the ground. The instructor should, if practicable, have
several counters taped out on the ground with the particular purpose
of showing the class how the contours run up the valleys and around
the spurs. He will also require each member of the class to trace
Figure I and, by following the text without reference to the other
figures, to interpolate the contours on his tracing. The instructor
will point out errors in method; particularly will he see to it that




FIGURE II

interpolation be made along the main stream lines first and then along
the tributary streams and that interpolation is along ridge lines,
as the ridges point.

LESSON H.

MISTAKES IN DRAWING CONTOURS.

19. The characteristics of contours most frequently violated are
listed in paragraph 20. These characteristics must be studied in the
light of what has been said in Lesson I. There is no particular purpose
in one's committing these rules to memory. What is necessary is that
the beginner learn the reasons why contours have these characteristics.
On Figure V notation of contour characteristics are noted by numbers,
which refer to subnumbers of paragraph 20. It will be noted that
the main stream is shown much steeper in its lower reaches than
upper. This might be so, but is unusual; therefore should not be



8



TOPOGRAPHY, MAP READING. AND RECONNAISSANCE.



so shown unless indicated by data on the skeleton. Contours
marked 6 should turn up the stream lines. Contour marked 1
crosses same stream twice. It can not, therefore, be a level line, as
the stream has some fall. What is 3, a summit or a depression?
Contours marked 11 follow no system whatever; -ground shaped by
water erosion will not be thus. The one marked lla (if it be a con-
tour) indicates that one can walk directly across country from one
stream to another on a level line. Would the streams be here if
this were possible? Imagine yourself walking on contour marked
12; will you always have lower ground on the same side ?



90




FIGURE III



CHARACTERISTICS OF CONTOURS.

20. (1) All points on any one contour have the same elevation.
It is a level line.

(2) Every contour closes on itself, either within or beyond the limits
of the map. In the latter case the ends of the contour line will run
to itie edge of the map.

(3) A contour which closes within the limits of the map indicates
either a summit or & depression. In a depression there will usually
be found a pond or a lake. If there is no water, the depression must
be indicated in some way to differentiate it from a summit. A usual
method is to hachure the inner side of the depression contour.

(4) Contours never split and never cross each other except in the
case of an overhanging cliff, in which case there must be two dis-
tinct intersections. These cases are not common.

(5) Contours are spaced equally to represent a uniform slope.
If the slope is a plane surface (i. e., if it has no irregularities due to
erosion or other cause) the contours are parallel and straight.



TOPOGRAPHY, MAP READING, AND RECONNAISSANCE. 9

(6) In crossing a valley the contours run up the valley on one side
turning at the stream run back on the other side. In crossing a ridge
the contours run to the ridge line and, turning, run back on the other
side of the ridge.

(7) Contours are always at right angles to the lines of steepest \
slope. They, therefore, cross the stream lines and the ridge lines at J
right angles. *

(8) The contours are farther apart at the top and bottom of an
eroded Jiill than near the middle, because in these portions the slope
is somewhat flatter.

(9) Contours are usually closer together near the sources of streams
as a stream is usually steeper near its source. This is not always so.




FIGURE IV

A stream may have at its source a very flat collecting basin, a lake,
or pond.

(10) The larger the stream,, the flatter the slope in the usual case.
Hence, contours are usually closer together on tributaries than on
main streams.

(11) Bad shaping of contours is usually due to illogical interpo-
lation between critical points. Remember that the drainage lines
and ridge lines are master lines of your contours. Interpolate along
drainage lines first, beginning on the main lines and going to the
tributaries. Then search out your ridge lines and interpolate along
the lines of the ridges.

(12) If one has difficulty in tracing out a particular contour, he
may be helped by imagining himself to be walking along the con-
tour. If he starts out with low land on his right hand, he will always
have low land on his right hand as long as he walks that contour in
that direction and vice versa.



10



TOPOGRAPHY, MAP READING, AND RECONNAISSANCE.



PRACTICE WORK.



21. Figures VI, VII and VIII are sketches giving the drainage

net and critical points of three areas in the vicinity of Fort Leaven-

worth, Kans. The instructor will require each member of the class

f to trace these skeletons one at a time and to draw in the contours

I following the systematic method heretofore described.

There can be no better training for one who is studying topography,
sketching, or map reading. Not until one can complete a skeleton
such as these, with great readiness, is he able to take up the reading
of or sketching of topography. It is not considered desirable for
anyone to take up the study of Lesson III until he has mastered




MISTAKES IN DRAWING CONTOURS
FIGURE V

" logical contouring." It may be necessary, therefore, to devote an
additional lesson period to practice in drawing contours.

LESSON III.

SKETCHING.

22. The instruments issued by the Engineer Department for sketch-
ing are based on the plane-table method. They are simple. Skill
in their use can not, of course, be acquired without practice, but one
can begin to use them with very little preliminary instruction.

It is the beginner's lack of a general plan of operations, his lack
of appreciation of the essentials, his waste of effort and patience on
the nonessentials, that make sketching the l&te noire of a soldier's
training, rather than the admitted inaccuracy of hand instruments
and his lack of skill in their use.



TOPOGRAPHY, MAP READING, AND RECONNAISSANCE.



670



860



810)



797*



870




DRAW 1O-FT. CONTOURS ON THE ABOVE SKETCH

LOWEST CONTOUR 79O

FIGURE VI



12



TOPOGRAPHY, MAP READING, AND RECONNAISSANCE.



The following plan of operations, if adhered to, will produce good
work. It would be well if the instructor could select an area and
lead his class around and through it as described, explaining the text
to them as they proceed from point to point. The first step to be
taken is to prepare a skeleton of the area entirely similar to those
shown in Figures I, V, VI, VII, and VIII. The next step is to draw
the contours and finish the sketch in all of its details.



.917



960



962



930



x880




780



DRAW 20-FT CONTOURS ON THE ABOVE SKETCH
LOWEST CONTOUR 78O

FIGURE VII

PREPARATION OF THE SKELETON SKETCH.

23. We have learned from our practice in drawing contours what
lines and what points are essential on the skeleton. The problem
now is how best can these be located. It would not do, of course,
to attempt to traverse out every stream system and every watershed
to its minute details. This would take forever, and would be con-
trary to the first principle of all mapping, which is to treat the area
as a unit; "proceed from the whole to the part." There are several
good methods of procedure, but most of those usually explained are
for the use of the man who has already become a good sketcher. The.



TOPOGRAPHY, MAP READING, AND RECONNAISSANCE.



13



following method is for the beginner. It may be modified as he
becomes more expert.

24. First, traverse around the area, returning to the point of begin-
ning. In traversing, locate

(a) Every drainage line crossed or which runs along generally
parallel to the line of the traverse and note the direction in which
the stream flows (or the dry creek drains) . This is absolutely neces-
sary.

(b) Every house or other easily identified feature near the road,
which will enable the sketcher later to identify himself on the sketch.



MO PERCEPTIBLE FALL
WITHIN THE LIMITS OF
THE SKETCH




780



DRAW 2O-FT. CONTOURS ON THE ABOVE SKETCH

LOWEST CONTOUR 73O

FIGURE VIII

(c) The high points between drainage lines, i. e., the point on the
ridge line where the traverse crosses the ridge line and a point or
so on each side of the traverse on the ridge to locate the ridge line
as well as may b possible.

(d) Determine the elevations of all of these points. Do not draw any
contours yet. Even the experienced sketcher should be slow to put
in contours until he has reconnoitered enough of the area to pin
down the drainage system. He must wait until lie has seen enough of



14 TOPOGRAPHY, MAP READING, AND RECONNAISSANCE.

tlie country to know how the big features lie. The little ones will take
care of themselves later as the work progresses.

25. Second, adjust the traverse. When in the circuit traverse the
sketcher has reached a point from which the point of beginning can
be seen, it will be found that when the instrument is oriented the
ray to the point of beginning on the ground will not pass directly
through the point of beginning as plotted on the paper. This is to
be expected. If the error in direction is not out more than a degree,
let it go at that for the time being and pace the distance to the point
of beginning. Lay this distance off on the ray as actually drawn.

There witt be an error of closure. If there has been no opportunity
to check orientation or distance in the circuit, it will be good work
if the closing error is not greater than 5 per cent of the entire length
of the traverse. Providing the error in direction can not be accounted
for by local attraction at any point, nor the error in distance by incor-
rect plotting of any course, distribute the error by moving points of
traverse.

26. It will not be necessary to go into refinements in this adjust-
ment. Move the last point up to the point of beginning; the next
to last point but one hi the same direction but a lesser distance, etc.
Be sure in doing this that no two courses have a plotted angle between
them which differs noticeably from the actual angle on the ground', other-
wise your sketch will mislead some one. The sketch must have no
misleading errors. It will have errors, but they must not be those
which win mislead.

27. Third, traverse through the area. The sketcher has now been
around the area. He has located all the water that flows into the
area and all that flows out. He has tied down his drainage system
pretty well. He will have noted the relative size of the streams or
drainage lines and their elevations and this will give him a good
idea as to which ones are the main drainage lines of the areas. He
must now find out how these drainage lines connect up inside his
area. In open country he may be aole to locate the stream junc-
tions in the interior by intersections from the traverse. Ordinarily,
however, these stream junctions are hidden by tree growth or folds
of the ground. It never does in sketching (at least for a beginner
and seldom for an experienced man) to guess how the drainage runs
through the area. There is no royal road to stream junctions.

If the sketch is to be a truthful report of a topographic reconnais-
sance, the sketcher must make the reconnaissance. Let him traverse
into the interior said find out what is there.

Here is where the bad misleading mistakes of the sketch made by an
untrained man are apt to be made. Contrary to a"ll advice he has
probably attempted to contour as he went along. He has drawn
in a number of ground forms as they appeared to him as he went
along on his circuit traverse. These forms are usually exaggerated
in size. Every hill looks big when one is on top of it. His forms
therefore project into his area much farther than they should. When
he gets inside, he must either rub them all out or change his drainage
lines, which he finds by reconnaissance to be thus and so to so and
thus to correspond to his badly built ground. The result is worse than
useless; it wifl deceive the user of the sketch.

28. The manner in which the drainage connects up inside the area


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