Further development in this direction can be expected and will mean an increase of 
quality and economy of reconnaissance mapping. 
Various technical groups became more and more aware of the photogrammetric 
technique and of its advantages. In consequence not only professional mappers but also 
those working in the field of civil engineering, forestry, geology, hydrography, geo 
graphy, etc. are using photogrammetry on a continuously growing scale. Thus from this 
point of view the last four year period was one of further growth and development in 
photogrammetry. 
ANSWERS TO THE QUESTIONNAIRE SUBMITTED BY COMMISSION IV. 
Following countries answered questionnaire submitted by Commission IV and in con 
sequence the summary below will refer to these countries only: 
Belgium 
Canada 
Chile 
Denmark 
England 
1. General. 
In the majority of countries, photogrammetric mapping is being carried out by both 
governmental and private mapping agencies. Out of fifteen countries covered by this 
report, only three seem not to have private photogrammetric companies. One country does 
not organize its own photographic flight service and has to rely in this regard on foreign 
help. 
In highly developed countries, the main photogrammetric activity is concentrated on 
large and intermediate scales, whereas in other countries small scale mapping is the main 
object of photogrammetric work. However, even in these countries, a general trend is 
distinctly directed towards the use of photogrammetry for larger and larger scales especi 
ally in connection with engineering projects and mapping of fast growing city areas. 
In the majority of countries, photogrammetry became an exclusive method of topo 
graphical mapping. The main reason why in a few other countries photogrammetry is 
not used to the same extent is the lack of photogrammetrists at the university and tech 
nical level and the difficulty of securing necessary capital for the initial investment. No 
doubt this last difficulty is due to the lack of understanding by official authorities of the 
economic advantages of photogrammetry and its various applications. 
2. Type and accuracy of ground control points and photogrammetricaly established minor 
control points. 
In. more developed countries the mapping in scale 1 : 20000 or 1 : 50000 is based 
either entirely on existing triangulation points and traverse points or on very rigidly 
controlled aerial triangulation. The accuracy of horizontal ground control points in the 
first case is very high and is of the order of ± 1 m — as the mean square error. Vertical 
control points established mostly by spirit levelling are precise within ± 0.10 to ± 0.20 m. 
Aerial triangulation is used for short distances only (few overlaps), with an accuracy 
ranging from 1.2 m to 5 m in planimetry and from 1.0 m tot 2.0 m in altimetry. 
In less developed countries with very sparse or no ground control points greater use 
is made of aerial triangulation or of slotted template method. Often photogrammetric 
methods are used to establish horizontal control points only whereas a more dense vertical 
control network is established directly in the field. If barometric determinations of ele 
vations are used an accuracy of ± 3 m is sought. Using the radar profile technique the 
same order of accuracy in favourable terrain is being obtained over very long distances. 
Finland 
France 
Germany 
Holland 
India 
Israel 
Norway 
Pakistan 
Sweden 
Switzerland.