on 
absolute orientation obtained during the flight. To the number of these elements belong: 
the determination of aerial photograph scale by radio-altimeter readings, the determin- 
ation of the angle of tilt of the base with the aid of the statoscope, and the determination 
of co-ordinates of the projection centre with the aid of radio geodetic devices. The tilt of 
aerial pictures is made considerably smaller through the use of a gyrostabilized aerial 
camera. In connection with the analytical control extension electronic computing 
machines begin to find their way into practice. 
The scale of aerial photographs is chosen as small as possible in comparison with the scale 
of the map being compiled. This decrease of the scale of aerial pictures is achieved by 
use of superwide-angle aerial cameras and of lenses of a higher resolving power, as well 
as by a better brightness distribution and lower distortion; by use of more reliable means 
of flattening the film, and, finally, by use of photosensitive materials characterized by 
a better stability of dimensions. 
Improved interpretability of aerial photographs is secured by utilization of colour and 
spectrozonal films: this permits to widely combine methods of office and field photo- 
interpretation. 
Owing to diversity of physical-geographical conditions in different regions of the 
USSR, as also to variety of mapping problems (scale of the map, accuracy, and volume 
of the work involved), instruments of different kind and various methods of plotting 
are to be applied in order to meet, in the best way possible, the requirements of every 
specific case. Thus, for instance, it is advisable to map flat-plain regions with the aid of 
superwide-angle aerial photographs, and to carry out stereophotogrammetrie plotting 
preferably on stereometers as they have a wide field of view, this method securing a 
more satisfactory, in geomorphological respect, representation of relief. And, vice-versa, 
mapping of mountain regions should be executed with the aid of normal-angle aerial 
photographs, and the map compilation and drawing of relief should be carried out on 
instruments of the stereoprojector type. In a similar way, methods of photogrammetric 
control extension must be correspondingly modified in accordance with the specific 
conditions of different regions. There can be no doubt whatever, that the present state 
of topographical photogrammetry is not to be considered as being definitive, because 
there still exist many possibilities of raising the efficiency of this work.