The sun., 1919-09-28
Government Experts Plan to Apply
Principles of War Time Aerophoto-
graphy in Mapping Regions Inac-
cessible or Hazardous ofApproach
by Land-Accurate Charts Vital
to Aviators asWell as Mariners
By ROBERT C. sKERRETT.


opinion that the airplane can be used
to advantage in helping us to deal
speedily with this shortcoming. But
est the man in the street Jump to an
unwarranted conclusion, Col. Jones
tells us: ut is not believed that the
uirplane unsupported by other survey
Ing can give the final accuracy re-
quired in original surveys. But by it's
means can be made map that will be
much better than the maps which may
be in existence to-day in the areas
which have not been geographically
mapped"
Doing Old Work over.
very considerable part of the
regions already traversed by the tran
sit man and his brother of the plane
table will have to be resurveyed. In
the decades gone there was not a fixed
system OF survey control throughout
the whole country, and5 the topogra-
pliers of the various States worked in
large measure Independently and with
out reference to common bench marks.
AS result, when these different topo-
graphic surveys and maps are brought
together gaps and other inequalities
are frequently disclosed. These dis
Crepancies make for confusion and
present serious difficulties when the
photographer tries to harmonize the
discordant features. This cannot be
done without giving due heed to the
correct geographical relations and 80
the rival property interests which may
be involved.
In order that the imperfectly sur
veyed portion of the country may be
mapped in the near future II is more
than likely that the airplane will be
called upon to do its helpful part, but
COL Jones cautions us that 1t would
be necessary to have a great amount
of triangulation and traverse run with
a view to furnishing the horizontal
control for the photographs to be made
by the airplane. With this control 1t
would be possible to fit tie photo
graphs on the map into their proper
positions" That is to say, the lines so
established or determined would cou-
stitute corrective network of known
distances and directions and thus
would evaluate accurately the data
obtained by the pictures taken from
aloft.
1t must not be imagined that II will
be practicable to make an extended
airpfane flight and at the same time
obtain photographs that will insure a
high degree Of precision in any maps
made therefrom. The best results VOL
probably be secured where aeropho-
Biography Is employed above successive
underlying areas of moderate extent
While we probably shall have to make
Roadway somewhat slowly in this new
field Of surveying lest mistakes be
made that would vitiate the work. still
American ingenuity and our recent
experience may confidently be counted
upon to provide methods and facilities
which Will add both to the accuracy
and to the speed with which these
activities can be carried on. Indeed.
it is already manifest that the air.
plane is going to be the means OF
saving the surveyor a vast amount of
labor, particularly in the detection of
physical changes and the rapid record
ing of an immense wealth of topo-
graphic detail.
The CeaseIessIy Changing shore.
AS most OF us know, the purpose of
our coastal charts is to furnish the
navigator sure guides in travelling I'D
and down our seaboard waters or
when approaching our shores from the
| open ocean. These charts are pre-
pared from data obtained by topo-
graphic surveys of the coast line and
of the area Immediately back of it,
combined with photographic surveys
or the contiguous waters. In the
course of the years gone our CONT
mental littoral has been mapped care
fully, but considerable intervals have
followed since much of this informa-
ton was last obtained, and nature in
certain regions has been restless. Az
consequence ocean currents and the
wash OF stor m tossed waves have
brought about radical alterations of
Inc coastal contours. Some of these
are SO momentous that 1t has been
quite out of the question to record
their annual notifications upon the
oNcial charts-nien could not be
spared from other work of the United
States Coast and Geodetic Survey to
measure these ceaseless changes.
Col. Jones points out as an example
the case of Fire Island entrance,
where shifting sands have modified the
approach by about sour miles in the
course OF the relatively short period of
five decades. AS he says:
The changes are SO rapid that fire.
quent resurveys Of the coast must be
made to furnish exact and reliable in
formation to the navigator. 1t is also
necessary to revise the area just back
from the coast, for roads frequently
are changed in position or abandoned,
new ones are established, houses are
built or burned, villages spring up.