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the reporting is generally done in terms of plasticity and compaction character- 
istics of various soils. As with every tool and device, aerial photography has 
specific uses and variable values in the different fields. In many areas it pro- 
vides details that are considered insignificant or refined beyond today's use. In 
other circumstances, the information derived falls below the minimum needed. 
In most instances field work of some type is required to confirm specific conclu- 
sions. The results of photo interpretation vary greatest in terms of the indivi- 
dual interpreter's skill. It is difficult for many to realize that it is not only 
"seeing" the picture, but also recognizing the association of various features 
appearing in the photos that is important. 
Rock identification in most areas goes along hand-in-hand with the iden- 
tification of the soil mantle. The applicability and accuracy of this work varies 
widely. The most highly developed stage of this work now includes the iden- 
tification of sandstone; silt, clay and sandy shales; limestone and cherty lime- 
stone; gneiss, schist, slate and serpentine; acid and basic volcanic rocks and prom- 
inent members of the granitic family. Within the identification of each of 
these soil and rock types, there is a large field of minor detail that varies 
largely with the interpreter and field of interest to which his work is applied. 
Basically, it forms the important detail of land evaluation and is amplified by 
land practices that are expressed in road conditions, fence conditions, size of 
fields and many other more or less dimensional factors. None of the work is 
done by formula, but is based upon observation, identification of soils, and judg- 
ment applied in the balancing of various factors. 
Experimentally, it has been shown that land classification done with aerial 
photography is equally accurate and infinitely more rapid than that done by 
ground methods alone. The trained interpreters are utilizing to some degree the 
two major fields of aerial photography: that of qualitative analysis dealing 
with the physical and chemical properties of soils and rocks, as well as the 
quantitative or photogrammetric evaluation of area and volume of ground 
features. 
The field of mineral inventories reports, in general, that the same features 
used in soil mapping are used in geologic mapping. The literature of the past ten 
years reports on the gross and obvious ground features that form striking pat- 
terns on the aerial photographs. Structural features, faults and the identifica- 
tion of certain limited types of rock are generally described. 
The need for special photography has been underlined in several articles 
on the subject. Although this field has been explored only tentatively, much 
attention is being devoted to developing techniques, methods, time of photog- 
raphy, scale, filters and other means of improving the quality and selectivity 
of photography used for this work. 
Those working in this field have found that aerial photographs record 
details of rock structure and associations of ground patterns that have not been 
observed previously because of the limited perspective available in field recon- 
naissance. 
The solutions to the problems of mineral inventories vary importantly 
with the climatic conditions of the area. The depth of soil and the amount and 
type of vegetation are important. The effects of arctic, arid and humid tropical 
climates place a shifting emphasis on such indicators as soil or rock and vege- 
tation. 
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
   
   
  
  
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