The principles and practice of map drawing, being in the main identical
with those of ordinary plan drawing, have been generally explained and
described in the preceding Sections. In the present Section, therefore,
we have only to direct attention to such details as belong especially to
the former class of topographical representations. These details relate
chiefly to the selecting of objects and features on the surface of the
ground whose character entitles them to special notice, and therefore to
distinct delineation; to the practical methods of sketching such objects
and features in the field, and to the means and the manner of
reproducing them on the finished map. The first and the last of these
questions have been treated by Mr. James in his Handbook of Topography,
and the second by Lieut. R. S. Smith of the United States’ Army, in so
concise and yet so complete a manner that we have not hesitated to avail
ourselves of their labours rather than attempt to offer any instructions
of our own. The following is, therefore, worthy of respectful attention.
_Single Stroke Streams._--In inking in streams, begin at the _source_
and draw downwards towards yourself, increasing the pressure on the pen
as you descend. The use of the steel pen in drawing single stroke
streams is very objectionable. Even soft steel pens are apt to cut the
surface of the paper, and in sharp bends it is quite impossible to
ensure an even width of line with the best yet made; by re-inking, much
time is lost, and frequently a rough jagged line is the result. The
common quill pen finely pointed will work well on any sort of paper.
_Double Line Streams and Rivers._--In maps of a small scale from 8 to 32
miles to the inch, it is usual to darken the north-western bank,
supposing the light to fall from the N.W. corner of the map; but on maps
of a large scale it is usual to attend strictly to the height of the
banks, and the draughtsman should carefully represent the exact nature
of each bank on his field-sketch or plane-table sheet.
_Colouring Streams or Rivers._--Single stroke streams may be inked in
with either a dark line of Prussian blue, or a light line in Indian ink
may first be drawn and a streak of Prussian blue or cobalt run neatly
along it. Cobalt is much used both in single and double stroke
streams--it is certainly the prettiest and most lasting blue we have,
and the preference should be given it, as it imparts a high finish to
MS. maps.
In maps which contain much hilly ground, the streams should be drawn in
with light ink and a very fine pen at first, and be re-drawn with dark
ink or dark blue after the shading of the hills. Large rivers on all
maps published in England are now coloured with a flat-wash of cobalt or
Prussian blue. Some draughtsmen prefer shading rivers according to
bends, and keeping the shade as falling from the N.W., but this system
cannot be carried out on maps of a large scale, where the height of the
bank is correctly represented.
_Islands and Sand-banks, Sandy and Pebbly Beds of Rivers._--Islands
which are only visible at low water, on well-coloured maps, are usually
first washed over with a light shade of burnt or raw sienna, or a
mixture of raw sienna and light red; the last-mentioned colour does not
easily mix with water, and should not be used if any other can be
substituted. After the tint is dry, dot finely with light Indian ink or
dark burnt sienna. Sand-banks are coloured in the same way. Sandy beds
may be similarly treated, omitting the dotting if pressed for time.
Pebbly beds should first be tinted with a mixture of burnt or raw
sienna, then dip into a dark shade of burnt sienna any coarse camel-hair
brush, and splitting the brush by drawing it between the forefinger and
thumb, dot in the tinted portions. Care must be taken to avoid having
too much colour in the brush, or the dots will run into each other and
make ugly daubs.
Another very easy and successful method of dotting in sand or pebbly
beds is with a tooth-brush. First, on tracing or any other thin paper,
trace out exactly the limit of the tinted portion requiring dotting, cut
out these portions from the trace and place it correctly over the
original, dip a tooth-brush lightly into a saucer of colour of the
required depth of tint, and holding it in the left hand over the
uncovered portions, with the forefinger of the right hand or the blade
of a pen-knife, gently splutter the colour from the brush; when it is
necessary to cover a large space with dots, this will be found the
simplest and most speedy way of doing it.
_Roads and Pathways._--The main or trunk roads in any country should be
very distinctly represented by double and perfectly parallel ink lines,
coloured between the lines with lake or carmine. District roads
metalled, or those made between chief towns, should be shown by a single
line coloured with lake or carmine. Unmetalled roads and paths by only a
single line in burnt sienna.
The same system should be carried out in roads in a mountainous country,
and the draughtsman should give, either on the map or in the column of
remarks, such information regarding roads as is likely to be useful to
travellers or military authorities.
_Mountain Passes._--On large scale maps these should be distinctly
marked, and the windings of the road correctly shown. Along the _Pass_,
write the name in small lettering, and state whether it is practicable
for horses, or fit only for men on foot. On maps of a small scale, it
will be sufficient to show the pass by a zigzag line across the hollow,
with a note as above.
_Fords and Ferries, Toll-gates._--Fords should be carefully noted and
the name and depth of water during the rainy and dry seasons given, if
possible. The number of boats at every ferry should be correctly
ascertained, and noted on the map. Toll-gates may be shown on roads with
a light line drawn across the road, and the words “Toll-gate” be clearly
written on the side of the road.
_Encamping Grounds_, _Mile Stones_, _Wells_, _Springs and Tanks_, should
be correctly shown _and named_ on all maps.
_Telegraph Lines and Stations_ must be shown on all maps drawn to a
scale of four miles to an inch and upwards, by the usual symbol. On maps
of a small scale, show by dots or a thin line of yellow, giving a
reference under the title. The _Stations_ are of the first importance,
and should be represented by the symbol.
_Railways, Stations, and Termini._--Railways are represented by a strong
black line, with or without thin lines drawn at right angles to the main
line. They should of course be very carefully and accurately laid down,
as they form the chief feature in any country.
Stations are shown by well-defined circles, and the name given in plain
lettering. Termini are best shown by blocks representing the size of the
buildings according to the scale of the map.
Except on maps of a very large scale, jungle should not be shown over
_hilly_ ground. Representing such objects as trees, jungle or brushwood,
over plains or flat lands, on all ordinary scale maps, is very
necessary, and the exact limits of the jungle or waste should be
surveyed and correctly given by a dotted line, but over hilly ground it
would be impossible to do so without impairing the beauty and hiding the
features of the hill drawing. If it is actually necessary to make it
known that the hills have jungle on them, let a foot-note to the effect
be inserted amongst the remarks or under the title of the map. Under the
head of remarks or notes, it is always very necessary to state the kind
of jungle which exists in the surveyed tracts, for the information of
speculators and timber merchants, and for the guidance of the
lithographer or engraver. Notes on maps, whether statistical or
geographical, can never be too full; they are useful in supplying at
once information which could be obtained only from reading reports, and
frequently they render topographical details intelligible where there
might otherwise be doubt or misconception. They can be recorded in any
spare corner or blank space on the map.
_Size of Cities, Towns and Villages, and the different ways of
representing them._--It is of the utmost importance that all maps of a
large scale should show the size accurately of cities, towns and
villages. If the scale admits of it, the several blocks or groups of
houses with the roads between them should be correctly drawn.
_Sketching, Shading, and Copying Hills._--In sketching hills, always
begin by fixing--1st. _The drainage_; 2nd. Those features which are most
prominent, such as peaks, rocks, ledges of rock running with the strata
of the hills, trees remarkable for some peculiarity in shape or size so
as to be recognized from various positions, and any other objects likely
to help the eye in filling in the details; and lastly, sketch the
details, beginning always with the ground nearest yourself.
Endeavour to portray your ground faithfully--1st. By preserving the
direction and bend of streams as in nature; 2nd. By giving the run of
the ridges correctly; 3rd. By fixing the peaks, ledges of rock,
precipitous falls and flats carefully; 4th. By showing the saddles or
depressions between peaks, which can only be done by giving the peaks on
either side sufficient relief in shading; 5th. By attending strictly to
the true breadth of valleys; 6th. By suppressing all hollows with a
suitable depth of tint; 7th. By careful representation of the banks of
streams in the valleys; and lastly, by finishing shades and touches, in
which is comprehended the retouching with brush or pen work the entire
piece, strengthening the shade of the higher ridges and peaks to show
their relative heights, and suppressing the white tint along the ridges.
Many excellent draughtsmen are in the habit of leaving the ridge of
mountain ranges quite white; this is evidently a mistake, for, unless
the ridge of any range of hills is of one uniform height from end to
end, it cannot correctly be left white. Thus a wrong impression is
conveyed of the surface of the ridge, the white streaks look harsh and
are displeasing to the eye, and a stiff and unartistic look is given to
the finish of the drawing.
The means of communication, whether by roads or minor tracks, are
important, both for civil and military purposes, and should be carefully
inserted in the map. This can generally be done with facility in a hilly
country, as the fixed marks will be visible in sufficient number along
the road, so that the latter may be drawn in at once by plane-table
operations along the line of communication to be surveyed. In flat
countries, or where the view is circumscribed, it may be necessary to
resort to measurements and plotting; but should any case occur where the
fixed points of reference are far apart, the traverse system must be
resorted to, and the road should be plotted from computed co-ordinates.
_Field Sketching._--Field sketches are made with the lead pencil, and
may be drawn upon every page of the compass-book, or upon the alternate
pages, at the option of the topographer. In the former case, the
bearings and distances are recorded upon the drawing; in the latter, the
record occupies the left-hand page, and the sketch the opposite one. The
page for sketching should be ruled in squares, with blue or red ink,
forming thus an indeterminate scale, the length of the sides of the
squares being assumed at pleasure, according to the nature of the
ground. Both the record and the sketch are read from the bottom of the
page upward. Suppose the stations of the survey to be 100 feet apart;
then, assuming the side of the square to be 100 feet, commence the
sketch at the bottom of the page--in the centre, if the survey promises
to be tolerably straight; if otherwise, at some point to the right or
left of the centre, the reason for which will be explained directly. Let
the bearing from the first station, the starting point or zero, be N.
10° E. Draw a line from the bottom of the page upward; the side of the
square being assumed 100 feet, number the stations upon the squares as
far as the line is run, say 325 feet, and write the compass angle down
along this line. Let the bearing from the second station, or No. 1, be
N. 1° W.; draw a line, making, as nearly as can be judged by the eye,
the proper angle with the last bearing, and proceed as before. When the
page is exhausted, commence with a vertical line at the bottom of the
next one, marking upon it the remainder of the old bearing, and making,
by the eye, a new series of approximate protractions as before. If it
can be foreseen, as in most cases it can, that the line of survey will
be very crooked, bending, for example, from left to right, then commence
the bearing at the bottom of the page accordingly, beginning at a point
on the extreme right, and running it diagonally to the left, so as to
make due allowance for the great deflection anticipated in the next
bearing. Such cases may be foreseen in running around an inclosure, or
in following a curving stream or ridge. The advantages of the system of
squares in sketch books completely overbalance the one disadvantage,
which is, that the diagonal bearings will not make exact distances upon
the squares, while the vertical and horizontal ones will. It will be
remembered that the surveying book is designed to be exact only in its
_record_ and the general features of the ground, and that a slight
change of scale is not material, as it can be made exact when the survey
is protracted upon the map. By these approximate protractions, any page
of the book of survey conveys a very just notion of the bearings and
distances, and of the relative positions of the general features of the
ground. The first station being at the bottom of the page, note down, in
the space between it and the second one, all the features of the ground
passed over by the line of survey; as to whether it is cultivated,
forest, marsh, &c.; whether it is crossed by streams, ditches, &c., and
their width; if it rises or falls; about what degree of slope, &c. On
both sides of the line introduce, according to the scale, and their
distances, as judged by the eye, all topographical objects within sight,
such as buildings, roads, streams, hills, &c., &c., drawing them to the
scale if possible, and if they cannot be got upon the page, describing
briefly their nature and position. In sketching hills endeavour to
project as many horizontal curves as possible, which should be lightly
put in, and then the shading lines may be drawn over them. The degree of
slope should be frequently written down in numbers upon the sketch. The
names of localities, streams, hills, farms, &c., should also be entered.
Thus far we have supposed a measured line upon the ground, to which the
situation and dimensions of objects might be referred. It is much more
difficult to embody the relative positions and dimensions, where all is
left to the eye. Here a cultivated judgment is of the greatest value.
Practice alone can make a good sketcher under such circumstances. Rules
must, from the nature of the case, be few and general. In the first
place, all objects within the field of vision are presented to the eye
in _perspective_, whereas the sketch is to be a _plan_. The apparent
diminution of dimensions in distant objects must therefore be corrected
on the plan. For example, the windings of a crooked stream, or a road,
in perspective, are much exaggerated in retiring into the distance; they
must therefore be _straightened out_ in the sketch more and more, as
they are more removed. 2nd. In looking at variously placed hills from a
somewhat elevated station, the eye will in some cases look directly, or
perpendicularly, at the face of some slopes, while in others, the
surface of the slope, if prolonged, will pass through the eye, and will
not be seen in its true dimensions, though its inclination may be
judged. In sketching the shapes of hills, bodies of water, masses of
forest, &c., these facts must be taken into consideration, and to ensure
skill, eye sketches of a small portion of ground having well-marked
features must be frequently made, and compared with measurements of the
same features. In sketching a single hill, the best station is at the
summit. First endeavour to represent the lowest horizontal curve of its
surface; then a medial one; then the form of the level space at the
summit, or the highest horizontal curve. Others may then be introduced
between these, until the ground is sufficiently expressed. The angles of
inclination should be frequently noted down in numbers; all accidents of
ground, such as ravines, rocks, &c., should be carefully placed, and all
other objects, such as houses, fences, trees, &c., should be put down in
their proper relative positions and dimensions. Having thus prepared a
skeleton of horizontal curves, numbered as to inclination and heights,
the sketch will always serve a useful purpose without any lines of
greatest descent. After sufficient practice in this method, the eye will
become so cultivated as to enable the draughtsman to express the form of
ground by lines of descent at once, the mind conceiving the position of
the horizontal curves, and thus supplying the necessary data for the
shading lines, the relative thickness and length of which for the
different slopes is a matter very easy of acquirement. But this should
not be attempted until the method by horizontal sections is thoroughly
mastered.
It is easy thus to make a sketch of a single hill, but when there are
many, and the general face of the country is sloping also, the
difficulties of representing the connection of the different hills at
their bases are considerable. In such cases the direction and lengths of
the valleys, or water-courses if there are any, must first be noted,
bearing in mind the illusions of perspective in both its effects,
previously mentioned. Then establish the positions of the different
summits, marking down their relative heights, after which put in the
other objects to be represented, such as roads, trees, buildings, &c.,
referring their positions to each other, and correcting them where they
are found to disagree. Horizontal curves present the readiest means to
the beginner in sketching declivities. When, after some practice, the
form of a body suggests, as it always will, its horizontal sections,
then it will be time to resort at once to the lines of greatest descent.
The greatest difficulties to be overcome in the practice of
eye-sketching are, 1st, that of converting a perspective view into a
_plan_, in all its true proportions; and 2nd, in forming a just
conception of the intersections of different slopes _at their bases_.
Hence the rule, to project first upon the sketch, all the lowest lines,
or water-courses, and then the highest parts or summits. Then the middle
lines and objects may be placed, and the sketch filled up by referring
all others to those three groups which may be regarded as determined.
The lead pencil for field drawing should be moderately hard, and the
general tone of the drawing should be rather light. The shading of
slopes ought not to overpower by its depth the distinctness of other
objects, and the pencil should be so used and of such a quality as not
to be easily defaced by rubbing.
We have already described some of the duties of the “examiner” in
verifying and supplying detail in the field. The following fuller
exposition of those duties and the methods of performing them is taken
from an excellent little treatise on Land Surveying, by John A. Smith,
C.E.
_Examination of Maps in the Field._--For the purpose of the examination,
the “examiner” should be furnished with an elegant and accurate trace,
ink copy, of the plotted detail of the district, and he should be
provided with a suitable sketch case, lined with prepared ass skin,
pencil, linear scale, chain, &c., and labourers. The trace copy, in one
sheet, should be in extent not more than can be conveniently secured in
the sketch case. It is desirable that the marginal detail on the trace
copy shall be common to the adjoining sheets for examination. If the
district be extensive, and if there be no more than one examiner engaged
on the examination, adjoining sheets should not be given to the same
examiner, that the character of the examiner’s work may be ascertained
by independent examinations of the same marginal detail. In the
examination of the detail representation on a map the “examiner” should
be mainly guided by a few leading considerations; these are:--
1. The position of a straight line, or detail, on the map will be
correct when its actual and plotted position on the ground and map makes
equal angles with another known line and intersects it in a known point,
the position of which line and point on the ground has been previously
ascertained to be correctly represented on the map.
2. The line, or detail, will be correctly laid down--given in magnitude
and position--when its position and length on the ground and map are
ascertained to correspond accurately.
From 1 and 2 it will be seen--
_a._ That the point of intersection of two given straight lines on the
ground, and the corresponding point on the map, will be a given point on
the map, if the corresponding lines on the map be ascertained to be
correctly laid down in position. And,
_b._ That any two points being given or correctly determined, the
straight line terminating in them will be a given line. Further,
_c._ That a straight line traced or drawn through given points, is given
in position. It should be kept in view that lines may be more accurately
traced, and to a greater distance, with the naked eye, when the party
tracing is rather above than below the level of the field on which the
trace shall be made.
It may be also seen that a point on the map which is the common point of
intersection of three straight lines drawn through well-defined points
in the detail will be a given point, if lines traced through the
corresponding detail points on the ground be found to have a common
point of intersection. And further, that the correct determination of
two such points on the map determines, as already stated, the position
of a straight line through these points. The determination, in the above
manner, of three such common points of intersection correctly determines
the representation of a given triangle. In the examination the sides of
the triangle determined by intersections, as above, should be measured
on the ground, to ascertain and verify the accuracy of the
determinations of the angular points on the trace or map. The production
of detail lines, and lines traced through plotted points, should be
taken up in the chain measurements of the sides of this triangle.
Through these verified points straight lines should be traced, and drawn
in pencil, to well-defined points in the detail, such as the buttals of
fences, the corners of houses and walls, gate piers, &c. On these lines
the intersected and neighbouring detail should be examined by chain and
scale measurements. In the measurement of the lines the internal and
adjacent external detail should be very carefully examined, and
corrected on the map where found in error. The examination of the detail
should be carried forward by the production and intersection of given
lines, and also by chain measurements from given points, to verify the
position of the detail or other points on the map. This examination
should be continued to the limits of the trace sheet. In remote parts of
the trace and district, lines of verification should be drawn, traced on
the ground and measured with the chain to verify the scale measurements
by the examination. These lines should be long, and in situations
affording few facilities for the accurate determination on the map of
the position of the plotted detail by other modes of examination.
The straight line passing through the extremities, or other well-defined
points in curved detail, should be regarded as a detail line, and the
position of the intermediate curved detail verified by ordinates or
tangents. Buildings and adjacent detail should be carefully examined by
productions, &c., because of the greater difficulties these details
usually present to the surveyor and plotter, and the consequent
liability to small errors in the position of some of the plotted points,
which affect the direction of lines determined on them.
Among the Plates appended to this work will be found several examples of
map drawing suitable for reference. Plate 16 shows the signs used on
ordinary maps and charts. Plates 29 and 30 contain signs used chiefly
upon Indian and colonial maps; and Plates 31 and 32 give the signs
employed upon military maps, with a section and a plan of
fortifications. These signs should be neatly drawn and their dimensions
suited to the scale of the map, the same remark applying to these as to
trees in elevation. Plate 1 is a plan showing the principal characters
of work used in mapping. This plan has been very carefully compiled and
drawn to render it suitable as a plan of reference. Plate 12 illustrates
the construction and colouring of hills according to the several methods
described in the preceding Sections. Other examples, with rocky cliffs,
will be found on Plate 14. Plate 18 contains a piece of the Ordnance map
drawn to a scale of one inch to the mile, and furnishes an example of
finished work. Upon the same Plate will be found a piece of chart
showing soundings, intended as a reference for hydrographers and others
engaged in marine surveys. And Plate 28 shows the manner in which
geological maps are prepared. The whole of these examples will be found
worthy of careful study as specimens of the draughtsman’s art.
The Plates relating to this Section are Nos. 1, 10, 12, 14, 18, 28, 29,
30, 31, and 32.