ng of objec- 
valuable in 
throughout 
terials seems 
X air photo 
more often 
and criteria 
other con- 
y and other 
deposits. 
7 
> land form 
color tones, 
0 interpre- 
tained. For 
only large 
the states 
(9) is from 
reo vertical 
apparatus, 
projector, 
developed, 
planimeter, 
(639) 
wedge bars, photo keys, height finder, contour finder, stereoplotters, 
stereocomparagraph, multiplex or “Kelsh” equipment; stereoscopic pro- 
jectors which permit use of contact prints for planimetry, and low 
stalling-speed aircraft equipped with camera with extremely high shutter 
speeds and compensating film magazine. 
Some of the same equipment appears in both lists. This is natural because 
in the states where photo interpretation has made greater progress more equip- 
ment is used. The answer listed last under question 3b is from a state which 
used very large scale photography. To obtain sharp, high quality photography 
at such a large scale, a plane with low stalling-speed and equipped with a high- 
speed camera with compensating shutter would be desirable. 
4. QUESTION: “What photo specifications are desirable or necessary for the 
type of work under consideration, in terms of: scale; type of 
photo (vertical or oblique, single or multiple, or continuous 
strip); film; filter; and season of year?” 
Answers. 
Scale. — The scales vary according to the purpose. For reconnaissance 
work and geologic and soil studies, the 1:12,000 and smaller scales to 1:62,500 
are used to good advantage. The scale ratios between 1:2,400 and 1:12,000 are 
used for comparison of routes. For greater detail, the larger scales are used 
such as 100 feet, 160 feet, 200 feet, 400 feet, and 800 feet to one inch. The 
scale of 1:20,000 is most frequently reported. 
Type of photographs. — Most states use vertical photographs, a few use 
obliques, and one or two use vertical continuous strip. 
Film. — Replies vary. Most states report using high-speed, low-shrink 
film. Listed are: panchromatic; super XX aerographic; high-speed low-shrink 
and fine-grain film; and safety-base, low-shrinkage film. 
A few report leaving the choice of film to the contractor taking the photo- 
graphy. 
Filter. — Filters mentioned are yellow haze and minus blue with yellow 
haze filter being mentioned more often. 
Season. — Most states prefer a time when trees are devoid of leaves and 
when there is no snow on the ground. This means early spring or late fall for 
most states. Two Gulf states prefer winter. One state reports summer for foliage 
definition. Another state prefers a time when both heat waves and snow are 
absent. 
5. QUESTION: “To what extent has color photography been tested, and with 
what results?” 
Answers. 
Most states report they are not using color photography because it is too 
slow and too expensive. One commented that transparencies are hard to work 
with. Successful use of color obliques is reported in one case. Another state 
reports extensive tests with color film interpretation where highway strips were 
flown and photographed with a Sonne continuous-strip camera. 
49a