Figure 2. Map of area shown in figure 1. 
For a description of each of the homogeneous units encircled on this map 
and on the photograph, see text. 
zz 
\ 
  
, an elemental hydrographic unit, 
vegetation unit and a basic functional-economic unit. Compare 
Figure 1. Vertical aerial photograph of an area on which have been delin- 
with figure 2. 
eated an elementary morphological unit 
a basic 
  
  
REPORT OF COMMISSION VII 95 
cut into the tuff and lower strata of the terrain. The basic functional-economic 
unit reveals how man has developed the terrain (human imprint). 
Photographic interpretation of the vegetation types or associations within 
an area is largely influenced by: 1. the photographic film-filter combination 
employed during photography: 2. the scale of the photography; and 3. the 
available information relative to the environmental conditions witbin the area 
photographed. Seasonal aspects of vegetation cause variations in the appearance 
of certain vegetation types on aerial photograps. In areas containing both de- 
ciduous and evergreen trees winter and fall photography permits differentiation 
between these two groups and also facilitates the interpretation of details in the 
forest understory in deciduous stands. However, because of local variations in 
climatic conditions, not all trees of a given deciduous species will be at precisely 
the same seasonal state, particularly on fall photography. This fact often makes 
species identification very difficult on such photography. The same condit’on 
usually prevails on spring photography. However, spring photography, like that 
taken in fall and winter, usually permits a ready distinction to be made between 
deciduous and evergreen trees. From the standpoint of tree species identifica- 
tion, summer photography often is preferred because the foliage of the trees has 
reached in this season its normal coloring. 
PHOTO INTERPRETATION EQUIPMENT. 
In my judgement, the indispensable instruments for a photo interpreter to 
be able to carry on his work are: 
(a) 1 direct vision stereoscope 
(b) 1 stereoscope that can measure horizontal parallax, and with the help 
of a pantograph reducer, offers the possibility to reproduce graphically, 
the particulars observed in the photographs and to perform little plani- 
metrical sketches. 
(c) 1 micrometrical lens 
(d) 1 wide range lens 
(e) 1 reduction compass 
(f) 1 calculation rule (slide rule) 
(g) various drawing materials, such as: dermographic pencils, ordinary pen- 
cils, rubber, china ink, squares, triangles, various compasses, etc. 
I consider it useful to attach to my report the description of a stereometer, 
known as the Stereomicrometer O. G. which offers in comparison to normal 
stereomicrometers several important advantages. 
As seen in figure 3, the Stereomicrometer O.G. consists of two boards, S 
and D, connected by a hinge which permits them to be closed like a book. On 
each board one of the photographs of the stereogram under examination is fixed 
‘by tacks. The hinge which connects the two boards has a groove, A, which 
serves originally as a supporting guide for a glass plate, B, on the lower surface 
of which a line has been engraved which is perpendicular to the groove, A. With 
this device it is very easy and quick to orient reciprocally the two photographs 
according to their respective nadir points. After the glass plate has been taken 
away, one can mount the stereoscope, provided with a mirror, on the board, C 
and observe the stereogram in its entirety. In case one wishes to examine some 
particular detail or measure parallax, the stereoscope is taken off and a stereo-