subserve are the following: the valuation of property for the
equitable adjustment of taxation and assessment; the sale and transfer
of land and the registration of title; railway and other civil
engineering work, such as the construction of roads and canals, large
sanitary and drainage schemes, military engineering works,
hydrographical, geological and mineral surveys; the reclamation and
improvement of waste lands, and of land from the sea; transactions
affecting land as between landlord and tenant; statistical surveys,
the setting out and adjustment of parochial and other public
boundaries and so forth.
It has been amply proved on the best evidence that a map, with levels,
on a scale of something like twenty-five inches to one mile is the
smallest which can properly fulfill all these requirements.
In the organization and equipment of the Ordnance Survey, as it exists
to-day, no pains are spared to secure the utmost precision and economy
in its methods of field work and publication.
After more than a century of development and the completion of the
cadastral map, let it not be supposed that its mission is at an end,
for it is proposed to make a complete revision of all the cadastral
work at least once every twenty years.
This is rendered necessary by the constant changes in property
boundaries, and the growth of population--which may be gathered from
the fact that the city of London increases in population at the rate
of about 50,000 a year, and that eighty or more miles of new streets
are added in the same time.
II.
The Ordnance Survey of Great Britain as it exists to-day is a
remarkable Publishing Bureau, from whose presses are given the most
elaborate and accurate series of maps which any country possesses.
Maps not alone confined to the representation of the physical features
of the country, but containing every detail of interest or value for
civil or military purposes.
It has justly gained the commendation of the French that it is "a work
without precedent, and should be taken as a model by all civilized
nations."
The principal scales of publication adopted by the Ordnance Survey
are: (1) A general map on the scale of one mile to one inch. (2)
County plans on the scale of six inches to one mile. (3) Cadastral or
Parish plans for the whole country on the scale of 1/2500 or about
25-1/3 inches to one mile, on which one square inch on the plan
represents an area of one acre. (4) For towns of over 4000 inhabitants
a scale of 1/500 of actual length on the ground or 10-56/100 feet to
one mile.
On the latter scale the city of London with its environs could not be
well shown on a sheet of paper less than 300 feet long by 200 wide.
When the facts are taken into consideration, that the Ordnance Survey
is a cadastral one, in other words, that one of its many objects is
the measurement and definition of all existing boundaries, political,
municipal, parochial or private, and a survey and valuation of
property for assessments, that its maps are accepted in courts of law
as authoritative on such questions, then the problem of the scales of
publication is the most important one to be considered.
As an illustration of the relation of the scale of a map to the amount
of detail, which can well be represented on it without confusion,
assume for a moment that an observer is stationed in a balloon, which
can be raised or lowered or placed at any desired height above the
ground, and in addition that he is provided with a horizontal screen
on which he is able to trace the details of the landscape below. The
eye of the observer well represents the lens of a camera, and the
screen the focussing plate. Therefore to produce a perfect image or
map of the ground below it will be necessary to assume that all parts
are stationary, balloon, plate and eye. For convenience assume that
the eye remains over the centre of the screen at a distance of two
feet. At a height of four miles above the ground the scale of the
image on the screen would be exactly six inches to one mile, or a
reproduction of the popular county map, on which every detail of
importance such as houses, roads, paths, and fences is shown, and the
smallest scale on which any attempt is made to preserve the relative
proportions of such details.
On such a scale the 1/100th part of an inch represents a distance of
very nearly nine feet on the ground and consequently however accurate
the map might be in its projection, as an image showing the relative
positions of all objects of importance on the ground, the scale is
clearly too small for the measurement of areas for valuation purposes,
and it is but a reproduction of the larger cadastral map.
Again assume that the balloon is stationed at a height of twenty-four
miles above the ground, and that the observer places his eye at the
same distance of two feet above the screen and attempts to construct a
map from the image on the screen, which is now reproduced at a scale
of one mile to one inch, or the exact scale of the general map. It
needs but little imagination to foretell that houses would be mere
specks, roads, faint lines, and forests, masses of color, in other
words, that it would be more instructive to consult the general map,
on which all details are magnified to be clearly visible and
topographic features brought out with great distinctness than to
attempt to trace with unaided eye, from the image of objects at a
distance of twenty-four miles, the course of streams or roads through
forest or moor, or to judge of the relative elevations or modeling of
the ground from the values of light and shade. Without an intimate
local knowledge of the county there would be nothing to indicate the
name or boundaries of villages, or estates or the political and other
subdivisions of the land, which are most clearly indicated on the map,
in unmistakable styles of lettering.
Another and more serious problem which would be lessened as the
balloon receded from the earth would be the distortion in perspective
produced by the irregularities of the surface. The higher points being
nearer the balloon would appear in the image on larger scale than the
lower, and only in the case of a perfectly level country, would it be
possible to produce a map without distortion by the method proposed,
and then only for a limited area.
As the balloon receded, the relative differences of elevation would
bear a smaller and smaller proportion or ratio to the distance, in
other words, the distortion would grow less until at an infinite
distance it might be neglected.
We might conceive that the observer was stationed at an infinitely
great distance, and provided with a series of magnifying lenses of
suitable powers to produce maps of any desired scale, yet, beyond a
limited area, he would still be confronted with the problem of
eliminating the distortion produced by the curvature of the earth.
Such is the conception of an accurate map which is an attempt to
produce on a plain surface or sheet of paper, a horizontal projection
of objects on the ground, which will show the relative positions of
every detail on any desired scale with as little distortion as
possible, and on which distances may be measured in any direction, and
areas computed with a degree of accuracy only limited by the scale.
When a survey of a small area is made, such as an estate or parish,
which bears but a small proportion in area to the surface of the
earth, curvature is neglected, distortion due to this cause being
imperceptible, but in the survey of a large country it is of primary
importance.
Returning to the conception of an observer stationed at an infinite
distance his position with reference to the new general one-inch map
of England and Wales would be in the plane of a meridian passing
through Delamere in Cheshire, and the published quarter sheets would
be a series of rectangles each 18 miles by 12 miles, containing an
area of 216 square miles whose edges were parallel to, and at right
angles to the central meridian.
Those of Scotland and Ireland have for each country a central meridian
and projection.
In viewing the county maps of six inches to one mile and larger
scales, it would be necessary to assume that the observer was
stationed over the center of each county except that, where two or
three counties lie so well north and south of one another, the same
meridian serves for more than one.
In the reproduction by photography of the maps on the scale of one
mile to one inch from those of larger scale, these facts, that
different planes of projection are used for the latter, have to be
taken into consideration.
In countries of larger areas than England it is more customary to
assume a central meridian for each sheet, in other words, the observer
would be stationed in the zenith of the center of each sheet and would
sketch but a limited area. The successive planes of projection,
represented by the maps, would resemble the facets of a diamond, and
it would be impossible to combine with any degree of precision a large
number together in one plane surface. On the other hand, the whole of
the one-inch series of England and Wales of Scotland or Ireland
register perfectly, and the distortion due to curvature cannot be
great, as the combined area of the three countries bears but a small
ratio to the whole surface of the globe.
Attention has been called to the fact that viewed from a balloon in
ordinary sunlight the minor features of topography become flattened
and indistinct.
If, therefore, we regard a sheet of the one-inch map held at a
distance of two feet from the eye as the picture of a country seen at
the distance of twenty-four miles, we see that details, that would be
invisible from above, are brought out with great distinctness on the
map and every detail of topography is shown in bold relief. In other
words the map is a diagram rather than a picture.
In the representation of relief on the one inch series, two systems
are common, contours and hachures. Contours represent the successive
shore lines which water at rest would form in following the modelling
of the ground at successive stages or elevations. If now we assume
that the water, having reached the highest point, is allowed to
retreat steadily to sea level the paths which the particles of water
would take from all points of the surface are those which the engraver
would endeavor to reproduce in the shade lines of a hachured map. In
addition he would adopt an arbitrary scale of shade increasing with
the steepness of the slopes, from white on a horizontal surface to
dead black on slopes of forty-five degrees, or greater, to produce the
effect of a model of the surface illuminated from above.
In the Irish maps this effect is bolder and more artistic, an
illumination from the northeast quarter having been carried out. The
shade lines still preserve the paths of particles of water in motion
on the surface, the color values being deeper on the eastern and
southern slopes, shadows have even been projected across valleys and
horizontal surfaces are in half tone, producing much the same effect
as the illumination of the country at sunset in midsummer.
The Irish maps exhibited are considered the finest specimens of
careful hill shading and will bear critical examination. For
comparison with these, other topographic maps are exhibited of many
scales and countries.
So far attention has simply been drawn to a few of the problems of
map-making, which are, briefly:
1st. The reproduction on a finite scale on a plain surface, of the
natural features of the terrain, with all the artificial boundaries
and objects added by man, so far as the scale permits.
2d. The extension of such a series of maps to cover a large area of
country still carried out with as little distortion as possible.
3d. The reproduction of such maps on suitable scales to meet all
demands.
If the conception is still carried out that the map, at a distance of
two feet, is but the image of the ground viewed from above, then the
cadastral map of England, from which areas of fields and estates are
measured for valuation purposes, would represent a view of the country
from above at a range of 5,000 feet or nearly one mile, and a town
plan, an image at 1,000 feet or a possible view from a series of
Eiffel towers.
This suggestion of an observer stationed in a balloon will not have
been valueless if it draws attention to the fact that vastly more
information is given on the map than it would be possible for any
single observer to discover from an elevated station with an
unobstructed view, the map being the compilation of the results of
hundreds of observations by many workers, and that its scale and the
amount and character of the detail shown have been specially designed
to meet definite ends.
It is beyond the limits of the paper to enter into the theory or
practice of surveying, or to say more than a few words of the delicate
and refined operations necessary in carrying out the geodetic or
trigonometrical work of a national survey which binds together the
many parts to make a complete whole.
The principal triangulation of the British Isles was begun in 1784 and
finished in 1852. Two magnificent 3-feet theodolites made by Ramsden,
one for the Royal Society, the other for the Master General of the
Ordnance, an 18-inch theodolite also by Ramsden, and 2-feet theodolite
by Troughton and Simms were used in these observations.
In the principal triangulation of Great Britain and Ireland there are
218 stations, at 16 of which there are no observations, the number of
observed bearings is 1554--and the number of equations of condition,
920.
In order to avoid the solution of this enormous number of equations,
containing 920 unknown quantities, the network covering the kingdom
was divided into a number of blocks, each presenting a not
unmanageable number of equations of condition. These calculations, all
in duplicate, were completed in two years and a half, an average of
eight computers being employed. Many of the sides of the principal or
primary triangulation are of great length, 66 of them exceeding 80
miles, while 11 measure more than 100 miles, the longest being 111
miles, that from Sea Fell to Sheir Donard. So great, however, had been
the accuracy of the observers' work, that the average amount of
correction of the observed angles was no more than 0".6, and the
measured length of the Salisbury base differed from its length as
computed from the Irish Base, 350 miles distant, by a difference of
only five inches.
The secondary triangulation interpolates points at shorter distances
apart ranging down to five miles, the observations being made with
theodolites of 12-inch circle. These triangles again are broken up
into smaller ones of sides from one to two miles in length, for the
use of the surveyor who is to follow and measure between the stations
with the chain; and a further subdivision of the trigonal spaces is
made in towns to points about 10 chains apart, where the survey is to
be made on the very large special scale. In the two last cases, 7 inch
instruments suffice for the measurement of the angles.
LEVELLING.
From 1839 to 1855, lines of initial levelling extending all over
England, Scotland and Ireland were run, and the observed altitudes of
the bench marks were reduced by the method of least squares.
In England and Scotland, these levels are based on the Ordnance Datum
at Liverpool, which is approximately the mean tide level of that
place; in Ireland, they are based on the low water level at Dublin,
which is about 8 feet below the mean level round the coast of Ireland.
The detail levelling is carried out contemporaneously with the
progress of the cadastral survey. Starting from the marks on the
initial series, lines are run along nearly all the turnpikes and
parish roads, and bench marks cut at intervals of about a quarter of a
mile.
The whole of the bench marks of the initial levelling are shown in
position on the 25-inch manuscript plans, and their heights given to
the nearest tenth of a foot. Surface heights, to the nearest foot are
also marked on the plans, at frequent intervals between the bench
marks.
CONTOURING.
Contrary to the custom in other countries, the contours of the English
survey have all been surveyed and levelled on the ground, checked by
the numerous bench marks, the standard of accuracy demanded in
levelling being two-tenths of a foot.
Owing to the expense of the process, about $1.25 per lineal mile, only
the 100 foot contours have been surveyed, except where greater detail
is required for military purposes, which information is not furnished
to the public.
HILL SHADING.
The hill features for the one inch maps are first sketched in the
field by the military method of slopes and sketch contours or proof
impressions of the contoured sheet.
Finished drawings from the field sketches are then made on cardboard
impressions from the one inch outline plates, and finished as guides
for the engraver to work by.
Beautiful and delicate in finish as is all the work of the copperplate
engravers on the Ordnance Survey, there is perhaps no branch in which
they so peculiarly excel as in their delineation of hills on the one
inch maps.
III.
It is impossible in the limits of a single paper to attempt to
describe the methods and processes of publication which are carried at
the headquarters of the Ordnance Survey at Southampton.
Carefully prepared treatises on the subject have been written by
officers engaged in the work, and for clear and concise description
none are better than the series of articles by Captain H. Sankey,
R. E., published in _Engineering_, in 1888.
There are two points of great interest in connection with the Ordnance
Survey which cannot be neglected. The one its military organization,
and the other the economy of its methods of publication.
Of its military organization, which has continued since the first
surveys were made for military purposes, it may be said that the
conservative precision of its methods of field work are best adapted
for military control and discipline. Under the successive
superintendence of highly educated officers of the Royal Engineer
Corps, whose patriotic efforts have been to secure efficiency and
economy in the service, the country has greatly profited.
Many of the improvements and inventions that have made possible the
publication of maps of all scales at the lowest possible cost, are the
results of experiments made by these officers.
It should not be forgotten in addition that as a branch of the War
Office and the Publishing Department of the Intelligence Branch,
military supervision is essential. Its offices are therefore not open
for public inspection except on proper introduction.
The author had the rare privilege of spending three months at the
Southampton office in 1888, through the introduction of the director
of the Geological Survey, and the request of our recent minister in
London, Mr. Phelps.
Nothing could have exceeded the courtesy and hospitality of the
director of the survey, Sir Charles W. Wilson, and the officers in
charge of the various departments, not alone in granting the necessary
authority to inspect every branch of the work, but in lending personal
aid and men for that purpose.
Great interest was also expressed in the topographic surveys of this
country which differ so essentially from the Ordnance Survey. In the
former, field work and methods are directly adapted to the scale of
publication; in the latter, the largest scale of publication governs
the operations of the survey, and the smaller scales are reduced by
photography, with a gradual elimination of unnecessary details from
the larger to the smaller scales until finally the topographic map of
the country, on the scale of one mile to one inch is produced, which
possesses an accuracy and character that could be obtained by no other
method.
To illustrate this important subject there are exhibited a series of
experimental and complete maps and diagrams which will well repay
careful examination. They were prepared and collected at the Ordnance
Survey at Southampton expressly for this purpose and with the kind
permission of the present director, Colonel Sir Charles W. Wilson,
R. E., C. B.
* * * * *
The author desires to state that many of the paragraphs of the paper,
particularly those relating to the history of the Ordnance Survey,
have been extracted from the following works and reports on the
subject:
1. The Ordnance Survey of the United Kingdom, by Lieut.-Col. P.
Pinkerton White, R. E.
2. The Ordnance Survey of the Kingdom, by Capt. H. S. Palmer, R. E.
3. Methods and processes adopted for the production of the maps of the
Ordnance Survey, by Lieut.-Genl. Sir Henry James, R. E., F. R. S.
4. Reports of Col. Colby and others in the Blue Books presented to
Parliament--1850-1860.
GEOGRAPHIC NOMENCLATURE.
REMARKS BY HERBERT G. OGDEN, GUSTAVE HERRLE, MARCUS BAKER, AND A. H.
THOMPSON.
MR. OGDEN: It was expected that Professor Mendenhall would be with us
this evening to address the society on the subject of Geographic
Nomenclature but he is unavoidably absent, having been called to
Philadelphia, and has requested me to represent him, and present to
you an apology for his absence.
Professor Mendenhall has been greatly interested in this question
since he assumed charge of the Coast and Geodetic Survey. Questions of
orthography and nomenclature have been before him almost constantly,
and the variety of views elicited in response to his inquiries
confirmed him in the opinion that the subject is of serious import. He
has had, of necessity, to decide a great many cases for publications
which were being made: finally a long list relating to Alaska came
from the Hydrographic office, which led to a discussion and the
suggestion that a board should be formed consisting of representatives
from the different departments and bureaus in Washington that were
interested in this matter, and that were issuing maps, charts and
other publications requiring geographic names. It is too true that the
different bureaus are now using the same names spelled in different
ways, sometimes different names for the same place, and the same name
for different places; indeed, the confusion is so great you may even
read publications relating to the same locality and at first not
realize the fact.
The object that Professor Mendenhall had in view in organizing a board
was to secure harmony; that all might come together; and that when a
question arose between different bureaus it might be referred to this
board to settle, with the concurrence of all. Such a board would also
secure stability, as no bureau would undertake to make changes in
names that have been accepted, as may now be the case when a bureau
falls under new management, or the determination of the questions is
referred to new officers without experience. This board, as proposed,
was to be formed by representatives from the Hydrographic Office,
Smithsonian Institution, War Department, Geological Survey, Coast and
Geodetic Survey, Light-house Board, The National Geographic Society,
Post Office Department, and the General Land Office. All these bureaus
or departments gave their assent except the Post Office Department and
the General Land Office; but we may hope that these departments will
eventually be represented, when the practical usefulness of the board
has been demonstrated by its decisions.
There are three, perhaps four classes of cases that cause the most
trouble in geographic names. In the first class, those cases where we
are certain of the name itself--that is, we agree in the
pronunciation, but disagree in the orthography; in the second class,
where there is no question as to the orthography, but where there is a
question as to what name should be used--that is, several names are
given to the same point, to the same body of water, or to the same
island; in the third class, where there is no question as to the name
or the orthography, but a question as to the place to which the name
applies--that is, there is no dispute as to the name, but it is
applied to different places; this class is sometimes modified by
questions as to the geographical limits to which a name applies--that
is to say, the area to be indicated by the name; for instance, some
body of water or a range of mountains, and may be designated a fourth
class.