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PHOTOGRAMMETRIC ENGINEERING 31 
PHOTOGRAMMETRIC ENGINEERING, Vol. V, 
30-42, 1939. 
8. Wieslander, A. E., and Wilson, R. C., ''Classi- 
fying Forests and Other Vegetation from Air 
Photographs,” PHOTOGRAMMETRIC  EN- 
GINEERING, Vol. VIII, No. 3, 203-315, 1942. 
Soil, CONSERVATION SERVICE 
An urgent need for reliable data regard- 
ing soil erosion, land use and other soil 
conditions led to Congress establishing the 
Soil Conservation Service in 1935. The 
major part of the more critical areas of the 
United States had never been mapped or 
classified for soil condition and the re- 
mainder was covered by small-scale or re- 
connaissance maps which for the most 
part were unsuitable for soil studies. 
The magnitude of the job soon proved 
that conventional ground methods were 
inadequate and in 1935 the use of aerial 
photographs for large-scale and accurate 
maps at 1:15,840 was begun.?%1% The first 
work covered 79 demonstration areas com- 
prising 5,273 square miles. Radial line 
plotting with hand templets of acetate 
was used to establish ground points and 
the map details were traced from the 
photographs to an acetate projection. 
The conclusion that this method was 
not wholly satisfactory led to one of the 
most important inventions in photo- 
grammetry, namely the development of 
the “Slotted Templet Method” in 1936 
by C. W. Collier of the Soil Conservation 
Service.'219 This simple device—a stiff 
piece of paper with radial slots cut into 
it—made possible the mass-production of 
photogrammetric maps at low cost and 
great speed. Today practically every 
country engaged in mapping uses this 
device in one form or another. 
Slotted-templet triangulation provided 
an economical method for making con- 
trolled mosaics. These mosaics proved in- 
valuable for study, planning and recording 
of soil conservation data. 
An overhead reflecting projector was 
designed and built by Soil Conservation 
Service in cooperation with J. G. Saltzman 
Company of New York for the transferring 
of detail from photograph to map. In 1940 
the Service added two Multiplex units to 
its equipment. 
The Service also pioneered in the use of 
high altitude, small-scale, photography for 
control purposes. In 1938 it used Coast 
and Geodetic Survey 9-lens photographs 
to extend control in sparsely-controlled 
areas in Texas, Oklahoma, Kansas and 
New York. In 1940 it used 4-inch focal 
length photography at inch-to-the-mile- 
scale, and thereby reduced the amount of 
field work by as much as 509. Small-scale 
photography for control extension also 
proved successful in providing supple- 
mental control used in conjunction with 
large-scale photography of the same 
terrain. 
The Kelsh Plotter, which turned out 
  
Fic. 1. The Magruder slotter and center punch.