Evening star. [volume] (Washington, D.C.) 1854-1972, 1930-11-23

IN NAN has discovered the world; now
III he is charting i-by airplane.
"A Within the last few years new
science has been evolved. Aerial
surveys have become an important
work, filed with unexpected Developments and
with remarkable possibilities.
BY using o camera and an airplane, two men
can accomplish the work Of accurate map
making IN much less time than a company OF
experienced surveyors. Over wild or unex-
pl0red territory the aerial surveyor can do o
lob that would be virtually impossible by work
ing along the ground
It took Mason and Dixon four years to sur
vey straight line between Maryland and
Pennsylvania, and their work was blocked by
Indians ut the end Of 244 miles. The chareng
Of o similar territory, under similar conditions,
b an easy task for the modern aerial surveyors.
The idea Of making maps from the air came
with the development of the airplane. All
maps, since time immemOFial, have been rep
resented as views from above. Mapmaking
from the ground Is q laborious task at best.
with the ahplane as the means Of proper OBJ
seTvation, the camera naturally took its place
as the recording instrument. The problem Of
covering territory depended entirely upon num-
cross photographs each a portion Of the nm
tshed map, and the experimenteTS IN aerial
survey soon found ways and means Of doing
their work effectively.
the aviator. He must choose his flight lines
They are taken, If possible, from old maps. The
pilot Of the airplane picks an object toward
which he directs his flight. He keeps as close
as possible to the straight line. He maintains
regular cruising speed and holds his ship at
o constant altitude.
he covers the territory which is to be mapped
BY flying back and forth, each line Of straight
flight being parallel to the original line. Thus
his whole hight-or series Of hightS-can be
traced by a series of parallel lines at o uniform
distance apart.
The cameraman is also ON the Job. He takes
his shots" at regular intervals so that he OBJ
tains succession Of photographs. The PIC
lures are taken so that each will overlap the
next one to an extent of 60 per cent.
The finished work goes to the engineers. They
examine the prints, paste them together and
form the complete map. Here the so per cent
overlap shows its advantage. Only the cen.
tiers Of the photographs need be used. They ut
together like the sections of q simple eut-up
puzzle, forming one clear entire picture Of the
territory which has been photographed.
The process Of aerial survey automatically
takes care Of certain problems In mapmaking,
chief Of which Is the matter Of scale. The
aviator picks an altitude, depending upon the
type Of camera used, and the pictures taken
from the height give the desired scale For
example, II q camera with an eight-and-oue-
quarter-inch lens is used, the aviator, by flying
at height Of $4,000 feet, enables the camera
man to produce a map that records 500 feet
10 the inch
Maps may be made at any height ND to
$1,000 feet. but most flights are made at an
altitude Of from 5000 to $4,000 fest. The fire.
quency Of photographs depends upon the altd-
tude: at a low level the camerman may snap
10 pictures minute; at higher levels, one pic-
ture every IS seconds Il sufficient