The Portland daily press. [volume] (Portland, Me.) 1862-1921, 1890-06-24
AToPonRAPhIcAL MAP.
What Such Map Should Be and
How II Is TO be Made.

oO AANHuChSlJ maui W bOOO bopVSiaphiNdA
map that it seems advisable to describe just
what such a map should be, and to state
briefly how it is made.
The best typographical maps ever made in
this country, and as good ones as have been
made in any part Of the world, are those
upon which the United States Geological
Survey is now employed. The prime object
for which they are constructed is the define
alton of geological features 1t is found,
however, that map that will serve this pur-
pose Is sufficiently exact to meet the wants Of
the civil engineer, the military engineer. the
agriculturist, the naturalist and all other
students who make use Of maps In any part
of their work. The following sketch, taken
mainly from the Sixth Annual Report Of the
Director of the Survey, will serve to indicate
the methods used in the preparation Of such
a map. The organization executing the
work Is. first, an astronomical and comput-
ing corps, the officers of which are engaged
in locating the actual positions Of certain
principal and important points, like the tops
OF high mountains, etc; second, triangula-
tion division, engaged in locating other
points by means Of those whose positions are
and, third. a typographical corps, whose
business 1t is to finish the survey with the
aid of the srationsIestablished by the trlangu-
latlOn officers. All minor positions for the
details of topography are determined by the
methods OF ordinary surveying.
'The plan Of the map contemplates map
sheets Of three different scales, suited to the
requirements Of the various sections Of the
country, namely: 1:62500, 1:125,000, aud
:250000 The first Is approximately one
mile to the inch. the second two miles to the
inch. and the third four miles to the inch.
The considerations governing the scale are :
first, present or prospective density Of settle
ment: second, economic Importance; third,
complexity of geologic phenomena; fourth,
degree Of detail In topographic features"
The map is constructed in contours, with
vertical intervals of 10, 20, so, 100, and go
feet, varying with the scale Of the map and
the magnitude Of relief features"
The map thus described will subserve
every purpose for which it may be used.
On the scale of mile to the inch the loca-
tions of points $50 feet from each other can
be readily represented. Prominences ten
feet in height. If the grade to and from them
is gradual, are scarcely recognizable in ma
ture. They are, however. detected and are
indicated on the map. BY comparison of
the vertical elevations of different points,
ahe slope Of rivers surface may be readily
ascertained and the amount Of power avail
able for use may be easily calculated. BY
carefully noting the amount of ground COW
cred by an elevation, and the number Of
elevations along a certain line the exact
amount of excavation and filling necessary
to reduce the grade for railroad construction
may be determined by the railroad engineer
without leaving his Office.
But In order to make the knowledge gath
cred by surveyors available to the people,
these maps must be so published that they
may be understood by the untechnical man.
The objection to many Of the foreign ordi-
nance maps is that, excellent as they may be
they are so filled with unnecessary detail
that tits with the utmost difficulty that man
unskilled in the use Of maps can learn from
them that which he desires to know. The
government maps are engraved in sheets,
each one covering degree Of latitude and
longitude. In the four mile scale one sheet
(the size Of which for Maine is about IS in.
by IS in,) covers 5000 square miles; in the
one mile scale 225 square miles are repre-
sented on quarter sheet of the same size as
the degree sheets. rhe water courses and
swamps are printed in blue, the contour
lines in brown, and the roads, railroads and
public culture, such as postoffice sites,
schoolhouses, ETC., in black. The maps
make fine appearance and are to be relied
upon for accuracy.
The extent of the public domain, its rela-
tions to contiguous countries; the bounda-
ries Of States, counties, towns, ETC., the posi-
tions ON the earth's surface Of cities, towns,
highways and other public cultural features
the creeks, rivers, lakes, coast lines and
other photographic features; the noun
tains, hills, valleys, plains and other topo-
graphical features are all represented on
such map, and are represented with such
exactness that DO one with ordinary intelli-
genee need fail to recognize them. For the
practical work in the field the country has
been. divided into areas embracing 225 square
miles and bounded by quarter degree lines.
Each year parties are sent out into the vari-
GUS districts for the purpose of establishing
stations where they are needed, or to plot
the country, making use of such stations as
are already established. Up to the present
time the survey has been able to use the tri-
angulation points located by the ceast survey
and have in this way been enabled to work
rapidly. Since the coast survey, however,
established no points not necessary for the
purpose of plotting the coast lines, the aid
to be ATTAINED from their work is necessarily
limited. No other surveys Of sufficient accu
racy for exact map making have ever been
attempted, so that the geological survey will
soon be compelled to enlarge its astronomi-
cal and triangulation corps, and so will be
required to contract its work in other direc-
tions, as much of the money which Is now
spent in tine ordinary processes Of surveying
will be needed for the expenses Of the other
two divisions.
1t will be noticed that the expense of con-
structing good typographical map must be
great. The average cost Of the maps thus
far produced by the government is about
five dollars per square mile OF country sur
veyed. With the additional cost OF trian-
gulation, necessitated by the progress OF
the work inland, the average cost Of map
making, like that described above, will
henceforth be nearer ten than five dollars.
But when such map is completed and pub
lished, it viii serve.for many uses for many
years, and can easily be modified and cor
rected at small expense, so that in the end
its cost Is much less than that Of an inaccu-
rate map in which less money may have
originally been spent. Measured by the
cost Of similar maps in other countries, the
United States Survey has done some excel
lent work in a very economical manner.
In the next letter an attempt will be made
to show what the Survey has done toward
she construction of a map Of Maine, and rea
tons will be given for the apparently slow.
work in this direction.
w. S. BAYLEY.