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western region had already been partially solved by terrestrial stereo photo- 
grammetry and the development of a plotter by Deville of the Canadian Topo- 
graphic Survey in 1896. But it was not until the early 1920's that aerial photo- 
graphy and photogrammetric map making began. Since that time nearly four 
million photographs suitable for mapping have been taken by the Royal Cana- 
dian Air Force, the American Air Force and civilian agencies, and are on file in 
the National Airphoto Library in Ottawa, which is a branch of the Department 
of Mines and Technical Surveys. This coverage includes verticals, tri-metrogon, 
tri-camera, continuous strip, and obliques. Scales vary, but very large areas 
have standard coverages at 1” = 1320’ (1/15,840) and 1” = 2640" (1/31,680). 
It is of considerable technical interest that the former scale has long been con- 
sidered in Canada the best compromise with regard to identifiable detail for 
forestry an other purposes and cost of coverage. For planimetric and topographic 
mapping at plotting scales of 1/31,680 and smaller, the 1/31,680 photos are 
considered adequate, and during the past few years 1/63,360 photos have been 
used for this work with a marked saving in cost of photo coverage. With the 
exception of very small areas restricted because of military or scientific instal- 
lations, all photo coverage is available to the public through the National Air- 
photo Library and the photo establishment of the R.C.A.F. where all negatives 
are stored and all prints are made on order from the Library. Many of the Pro- 
vinces maintain similar libraries for the use of their Departments and the 
public. It cannot be overemphasized that this easy accessibility has been a major 
factor in the growth of the use of airphotos in Canada, particularly in the 
fields of geology and mining. 
The Geological Survey, now a branch of the Department of Mines and 
Technical Surveys, pioneered the use of airphotos in field and mining geology. 
However, the Topographic Survey, another branch of Mines and Technical 
Surveys, pioneered terrestrial photogrammetry and is now the largest user of 
airphotos in the Dominion. Referring to the matter of scales mentioned above, 
it is estimated that the new 1/63,360 scale has reduced the number of photo- 
graphs passing through the department from some 115,000 per year to about 
51,000. 
All field parties of the Geological Survey are now provided with airphoto 
coverage of their areas as standard equipment for field work. Use made of this 
coverage ranges from navigational aids to avoid swamps etc. to extensive and 
intensive structural and geomorphic interpretation. It must be admitted that the 
number of identifiable bedrock geological features varies from nearly zero in 
heavily glaciated areas to nearly 100% in parts of the Canadian Shield, but it 
is the writer’s opinion that in general less than 75% of the possible use is ab- 
stracted from the photos by the survey parties. This figure is expected to im- 
prove as more stress is laid on photo interpretation in geology and engineering 
courses. 
In the field of Pleitocene geology alone, the use of the photo detail is con- 
sidered to be nearly 95% effective. This fact needs little comment, as glacial 
geomorphology approaches the ideal in photo detail. The old name of superfic- 
ial geology is very suggestive of the glacial features formed by easily compre- 
hended forces and as yet hardly touched by the agencies of erosion which so 
alter bedrock forms that their identification in aerial photos becomes a matter of 
rigorous deduction from nearly obliterated features. Pleistocene geology is be- 
   
  
   
   
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
   
   
  
  
  
   
  
  
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