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REPORT OF COMMISSION VII 27 
Current and potential wars have created an abnormal demand upon nations 
and groups of nations for natural resource materials and manpower. Military 
and governmental leaders need to know what they have to work with in terms 
of steel and food and lumber, as well as personnel. Inventories supply such 
needed information. Aerial photographs aid in many ways the procurement of 
accurate and economical inventories. Photo-interpretation, in turn, is the basic 
key to the fullest use of the photographs. 
Some of the recent advances in photo-interpretation can be credited to 
improvements in the quality of photographs. But of even greater significance 
is the fact that more and more workers are devoting themselves to the use of 
photos, and to the practical solution of problems which they encounter. For 
example, research foresters in the United States have succeeded in developing 
aerial photo volume tables for certain localities. The interpreter can study statis- 
tically located sample plots of a given size on the photos, and judge the species 
composition and density of the stand, and measure tree or stand heights and 
crown diameters. Entering the volume tables with such known data, an estimate 
of gross volume per acre can be determined. 
In recent years there has been a growing recognition of the interpreter’s 
needs in the setting up of specifications for aerial photography projects. The 
photo scale, the kind of film and filter, and the camera focal-length, can all be 
of vital importance to interpretation. 
Broad surveys, such as those designed to inventory large areas of timber 
land, or for soil or mineral reconnaissance work, can utilize photos of much 
smaller scale than 1:20,000. The multi-lens camera projects of the Canadians, 
employing both vertical and oblique views taken simultaneously, provide 
extensive coverage at low cost for their inventories of vast uncharted areas. 
Reconnaissance surveys of the soils and forests of Liberia, or of the Amazonian 
jungles, do not require large scales and the interpretation of minute details. 
Extensive coverage at small-scale provides the required detail, with less initial 
cost, and with less bulk in photos to be handled. 
Interpretation of small-scale photos is of necessity confined to a rather 
generalized segregation of broad vegetation types, such as forest, savannah, 
swamp, etc. Limited identification of vegetation species or ecological communi- 
ties may be possible, and tree heights can be measured with limited accuracy. 
Land forms and drainage patterns can be distinguished. Planimetric maps to 
serve as bases for the presentation of inventory information can be prepared. 
To get the most out of aerial photos, however, the interpreter needs scales of 
1:20,000 and larger. During recent years the trend has been towards obtaining 
photos of larger scales, strictly for interpretation uses, especially in areas already 
covered once by 1:20,000 or smaller scale photography. No maximum or best 
scale can be established for all projects, because each must have its own specifi- 
cations based upon the area involved, the kind and amount of inventory detail 
required, and other pertinent factors. Scales of 1:15,000 are now commonly 
specified for inventory uses. For special research projects, or for detailed work 
on small areas, 1:10,000 or larger has been used. Aside from the higher cost of 
such photography, inventory workers find that the added detail obtained from 
the photos does not offset the physical difficulty of working with excessive num- 
bers of prints, which have pronounced parallax and defilade, and scale variations. 
In recent years more work has been done on the problem of determining 
the films and filters best suited to particular needs. Both panchromatic and 
infrared films have definite advantages and disadvantages under certain condi- 
tions. Experimentation with color photography is being continued, but it still