1921-22 DEPARTMENT OF LANDS AND FORESTS 223 



The correct choice of machine to use is a matter having the greatest bearing 

 on the cost and results of the work. The requirements as regards performance 

 of machines will of course vary for different classes of work and in different 

 localities. But, in general, rapid climb is of great advantage as tending to 

 conserve flying time. Also a machine capable of high speed is more indepen- 

 dent of wind conditions and can with equal fuel capacity operate successfully 

 from the same base over a much larger area than a slower type. While actually 

 typing, however, it is found that when flying between 2,500 and 4,000 feet — 

 which is a satisfactory height from which to identify tree growth — the ground 

 speed of the machine should not exceed 85 miles per hour. By ground speed is 

 meant the speed at which the machine passes over the ground; it does not 

 correspond with the speed shown by the air speed indicator of the machine but 

 is greater or less depending on the influence of the wind. 



Observers. — This season there were two foresters with previous experience 

 both in flying and mapping, while a third was trained during the progress of 

 the work. Observers, to produce reliable type maps should have comfortable 

 working conditions in the machine, complete unconcern about the pilot and 

 machine, and the best base maps available. 



The quality of the map produced depends most largely on the experience 

 and judgment of the individual observer. This should not be confined entirely 

 to aerial experience, but should be checked by comparing aerial observation 

 with ground study of forest conditions. Too much stress cannot be laid on this 

 phase of the observer's work, and during the past season, whenever feasible, 

 landings were made as a regular part of the procedure in order to allow the ob- 

 server to investigate any stand of peculiar appearance, or to refresh his memory 

 as to the actual conditions of more familiar types. It was found also in this 

 connection that ground studies were of more value when made by the observer 

 in person rather than through the study of strip tallies, descriptions, etc., how- 

 ever full and precise. 



Base Maps. — Finally the field sheet on which the observer does his sketch- 

 ing should contain as much survey data as possible. This is even more necessary 

 in the air than in the same class of work on the ground, since it is not practicable 

 with the existing aerial instruments, to locate or orient the map in flight by 

 travelling on a known course for a known distance. Consequently the observer 

 is dependent for his location and judgment of distance and direction on the 

 detail of his base map. Experience in both ground and aerial mapping has 

 shown, however, that the aerial observer is in a much better position to work in 

 this way than the ground mapper, since he can see a greater number of refer- 

 ence points at one and the same time and is also (hills and valleys are not 

 apparent from the air) free from the difficulties arising from diff^erences in 

 elevations. Indeed, with a good base map, the aerial observer's work may be 

 compared to the copying — on a small scale — of a highly coloured carpet lying 

 beneath him, a great deal of the pattern of which, the base map detail, has 

 already been drawn. 



From the above it is readily apparent that the rate at which any given 

 territory can be typed is intimately connected with the completeness and 

 accuracy of the observer's base map, since a rational representation of the 

 timber types is usually dependent on these base maps details, particularly where 

 lakes and drainage systems are involved. Actual experience has shown that 

 for the above reasons, that is the relations between topography and timber 

 types, some additions to the existing topographic data — except in surveyed 

 townships — are always necessary before typing of timber areas can be com- 

 menced. 



