22 
The experiments made by the committee have yielded elucidating re- 
sults in many basic questions, and also in respect to. certain practical 
applications. In some instances, however, they have proved too limited. 
The experiments relate to vertical photographs chiefly taken during the 
summer. The majority of these were taken with wide-angle cameras on a 
scale of 1 : 20.000 with normal overlap. But to a lesser extent photographs 
have also been taken with normal angle cameras of various types, and 
also on large scales up to 1: 2.000. 
U. S. A.: 
(a) Companies that supply about 80 °/o of the timber cut of the U. S. A. 
use aerial photographs in one manner or another. 
(b) Instruments used usually are pocket stereoscopes principally — 
some mirror stereoscopes for height — parallax wedge, parallax bar. For 
crown diameters — shadow wedge or the equivalent. 
(c) For cruising — 
1) To delineate forest types and broad volume per acre classes on the 
photos. 
(2) To estimate by ground cruising or by measurements on the photos 
or by both means what the stand per acre is. 
(d) Precision: About 20—30 °/0. 
(e) About the least amount of saving in time is 20 9/o. 
(f) There is competition for greater accuracy in results. This means 
research and is to a large extent dependent on the economic conditions. 
As an example if there is mass unemployment and labour is cheap the 
companies will make limited use of the photographs and concentrate on 
ground cruising. If demand is high it may force existing mapping and 
interpreting companies to improve their equipment. 
Question No. 2: 
Determination of site and forest type. 
Finland: 
It is very difficult to distinguish by the aid of aerial photographs the 
Finnish forest types, which are based on the composition of the vegetation 
on the ground. However, especially in Northern Finland, certain types of 
forests are so predominant that only very little exploring of the ground 
is needed. Of all state forests and some other forests, maps and descrip- 
tions of certain regions were earlier compiled, on which the forest types 
have also been noted. 
Germany: 
Fitting into an already existing map, estimation by height classes and 
form of stand. 
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