East Oregonian : E.O. (Pendleton, OR) 1888-current, 1918-10-14
Marshall C
of Making Maps NJ IN War

after the trfangulation and isvsnE e.n ...A
done Of 4 certain area. that the toFaRS
engineer made q poiyconic projeofiou eN
scale desired for the map. then plo.lea
trfangulasion positions on the proiecta1ms So
then with plane table started the ro9a s9A1
Many oiviI snxsneeru DO not as YET asees.
eIate the power Of the teisseopic alleaSs - ~
plane TASTE as developed and used ~ IN
United states Geological Survey. AZ nay
stated. however. that in the hands cL -
perisneed topographic engineer this s.i,ssa -
strument for limited areas answers ~ -
needs Of Tho work in hand M
The theodolits trAnait and level wcsM @am
ali be done by the "plane table mesAA.4,t
The plane table = essentially dfswtns
board mounted upon tripod and with ~
it's parta 20 delicateiy made that Il can ~
placed IN any desired position @na~ R4t4
there. On II b stretched the heavily Eioaanse&
drawing paper upon which the entire NAP
IL surveyed. plotted and drawn up In to
neId
on this plane table Colonel Marshall hrfy
ther explained. the map is made by meanS
Of telescope sight and attached rui9Es
The mappsrs occupy one triangulation posi-
tiou and sighting or orientinE BY anotheK
point plotted on the protection. ann ~
sighting other points suen a. noeSes.
steeplss. road crossings, sharp peaks ana
SO on then move up to another point an4
orient back to the first point then sighe
the points sighted from the first point IN
this way they make Intersections which are
started from. this programme being CON
ttnued until the projection is closely COW
cred with locations.
To each OF these located points vertical
angles are read and then BY a single eo1npu-
tation the difference In the elevation 70 all
points IL quickly determined and the whole
is tied 10 level bench marks which In turn
have been tied By level lines to ma8n se9
level
The foregoing l. an outline Of The iaseFo-
mental part Of making a topcsraph.e map
and can easily be done BY any careful en-
gineer. The, work. however. Is to carry lines
Of equal elevation all over the map Tor
contour line is always a line closing - =
self. all points on The line being OF equal -
walton.
Imagine, II you can. the shore line e
lake. Raise or loWe= the lake dfEy fess
and the fontoEr Hne makes eounlDar une
fifty feet higheF o. lower as the ease nny
be from tho shore line before the lahe wns
raised or lowered; keep this up and ssenfu-
ally you have imaginary contour lines COW
orfng all OF the projections and you have =
contour map.
The real skfll in this connection conaa IN
being able to see the imaginary lines on the
uneven surface OF the land and to keep e
located. both horizontally and vertically. a
is very simple II one knows how and if iB
impossible IL you don't know how.
Among the many short cuts employed by
the map maker working a plane table are
sighting a graduated rod heid several hundred
yards away and reading through the teIN-
scope the distance without any ground uzeNGF
uring. taking sights from mountain and hill
tops and locating other points without goins
to them and also obtaining their differenna
In elevation without running lines' draw
ing in contour lines (Which differentiake tbs
entire form OF the ground by means Of 1ietia
more than q trained eye versed in Land foFmls
20 that their representation on paper ~
comes a very essential artistic adjunct IN ens
training: setting up shs piano table at an
location on the map and BY rnsana
of relative sights to known locations, dsteF-
mining the instrumental position on the map
at once and with no locations whatever.
In this wise the whole method In made
more or less mechanical and obvfates almost
entirely the keeping Of notes and OF writ
ing up the results ia the office at night. for
as above stated. the map Is made out og
doors and with the country to be mapped
before the engineer with the result that Il
Is made to represent the ground whiie tha
area to Be mapped is still spread out before
him.
After the map is finished II 10 brought to
Washington. and the draughtsmen ink In con-
tour lines in brown. In black the roads, houses.
&c, and In blue the water courses. thea IL Il
sent to the engraver and the copper plates are
cut. one for contours. one for roads. houses
and SO on and one for the water cournsn
Transfers from these three plates are put
on stone. and faster than one can count .
topogra phIc map is printed and you can uas
It for any purpose. for any out Of door plan
ming work