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174 INTERNATIONAL AMERICAN CONFERENCE.
additional ones on the sheet, bnt perhapG outside of the border. This gives one point
for each 60 sqnare kilometer (24 square miles.)
In the Prussian surveys 10 trigonometrical points are required for each 56 square
kilometers (22 square miles), scale of detail sheets "2ob-olf·
In Italy the scale used being ~' one trigonometricat point ]sdetermined for every
25 sqnare kilometers (10 square miles).
The heights ofthese points are also determinad and given to the topographer, who
bases on them his leve] or contonr cnrves.
The determination of points on which thc topographical survey depends has now
heen explained. Ifpossible, those determ>.I!ations sbonld be made in advance of
topographical work. Where that is impossible the topographer mnst leave perma–
nent marks in prominent positions, which are afterward detennined from the triangu–
lation.
On the Continent the topogra.phical work is done mainly with tbe plane table,
amount of detail introdnced depending on the scale adopted. Thus, in Prnssia,
where the scale of tbe plane-table sheets is ~' all necessary detail can be given.
Roads, paths, milis, detached houses, important fences, streams, ponds, forests,
bridges, mines-aH can be showu. \Vhen the scale is diminished to ooh-zr¡y, as in
Italy, a part of this detail must be 9mitted, and still more when the scale o"f publica–
tion is <liminished, as in Sweden, to ~·
In all the best modern surveys, even when hachures are used to give pictorial
e:ffect, the relief of the earth's surface is shown by level or contour lines, at eleva–
tions differing with the precision of tbe survey.
In the Prussian sbeets, scale ~6, the level curves are 20 or 25 feet apart in ele–
vation. The ... ')wio>s sheets, scale ~. give them 10 meters apart. In tbe Austrian
surveys at least eight heights are determined in each square kilometer for the scale
niJ-uo-, an<1 seventeen for the double scale. The level curves are at either 20
or 100 meters apart.
In the publication of the results of surveys, the scale r.s+oo, a.dopted by Prussia.
tbroughout, and by Switzerland, except for tbe most mountainous area, appears suf–
ficient for all purposes. It permüs the measurement of distancesto within 15
feet. It gives much more detai1 than the scaleof -¡¡-;dblf, at first adopted for the British
maps; and their map now being published on a scale of 6 inches to the mile, or nrJ-o-¡¡-,
while not large enough to give well the boundaries of eBtates, yet requires six times as
many sbeets as the scale nto-o- would do.
The scale nho furnishes also an admirable basis for detailed geological work, en–
abling tbe geologist at once to placeon maps of sufficient detail the resultsofhis labors,
as is being done in Prussia. Indeed, the general topograpbical and geological maps
of that conntry now in-fH'ogress present to us a standard of ex:cellence which can only
be attained after many years.
The detailed sheets need combination for general use into maps of a smaller scale.
General Dufour adopted ~ for bis excellent mn.p of Switzerland, and the same
scale is adopted for the general staffmap of Prussia, derived from the ~sheet.
In reference to the cost of these surveys per square mile, save in the case of Pr_us–
sia, there is little information. In that country there are about 200 square Pruss1an
miles (4,380 square miles) covered annually by triangulation, costing $78,000 gold.
The topography covers the sarue area per annu~n, and, with cartography, costs $117,000,
gold, per annum. Dividing the total expense, $195,000 gold, by 4,3 O, we have $44,
gold, per square mile as the cost ot tbe survey, exclusive of topography done by con–
trapt at tbe rate of 700 or 800 fraucs per square stunde, or $16 to $18, gold, per square
Englisb mile. The cost of triangulation, revision, and publication would
added to this. Half the cost of the new Swiss survey is borne by the Confederat10n
and halfby the cantons.
Publication on the scale of the :field-sheets only takes place when sorne society or
person agrees to bear halfthe expense. Austria expends annually about $4H0,000 _for
her surveys, but the area covered is not known. It is stated that in the A.ustr1an
surveys an officer oxperienced in topography can, with the aid of two or more ~ol­
, survey in tbe six sommer months, on a ~ scale, from 350 to 500 square kllo–
meters (140 to 190 sqnare miles), drawing the same in colors during the winter.
Schiavoni, in Principii di Geodesia, states that a topographer in six mon.ths can
complete 1 square kiloweters, the scale being Ylfh-¡,-. The wide di:fference m these
estimates is doubtless due in part to difi'"erence m precision of the work, althougb the
sca.les are nearly the same.
A writer in the North American Review of .July, 1875, estimates the . cost oí
the ordnance survey of Great Britaín up to that date at aboot 20,000,000, m gold,
and the area at 111,000 square rolle-. This would give a cost of "'190 per square mi le,
the work not yet being complete. It should be reruembered that it incluues many
public_ations on scale larger than nto-rr.
Takmg the Prussian survey a a model, ancl recollecting that the cost, $44 per
sq mlle, "!>ff r 8}:iWO. does not jnclnd.~ ~ht' yay of oft:ic~T 1 Mf (probably)