(360) 
5/100 mm and maximum 10/100 mm, the scale of the stereoscopic image is in 
general 1 :50,000 the residual errors are therefore mean 2.5 m and maximum 
5m. 
We do not insist on planimetric precision; the mean practical errors are in 
all cases less than 2/10 mm at the tracing scale; the maximum errors may reach 
3/10 or 4/10 mm if the errors of the control are considered negligible. The 
practical errors in altitude are furnished for the first two maps by the results 
of field completion after plotting. The contours present a mean error of 0.8 
for 1/20,000 and 1.5 m for 1 :50,000 maps. Among the points measured by the 
machine one finds 70 to 8096 with absolute errors equal or less than !/5 the 
contour interval (1 m at 1 : 20,000 or 2 mat 1 : 50,000). 
For the 1 : 100,000 map of the territories (Stereo Topographe type D) the 
following figures result from the errors of the control (barometric determina- 
tions) and the disagreements of the contours or measured heights of different 
models; mean errors 5 m maximum errors 10 or 15 m. These refer to 1 : 50,000 
film negatives. The planimetric errors of the plot of radial triangulation de- 
pending on astronomic points are mean absolute values, 0.5 m at the scale of 
the plot, or 25 m; the maximum errors may reach or exceed 1 mm (50 m). 
In summary the large universal plotting machines of the 1st order permit 
measuring the altitude of an isolated point with a mean error of 1 :10,000 of 
the flying height and drawing contours with an error of 1 : 5,000 of the flying 
height. These figures should be very sharply reduced if the negatives are taken 
on film. 
Organization of Plotting Operations. 
The practical organization of plotting offices tend to take a similar form, 
characterized by batteries of machines placed under the supervision of a photo- 
grammetric engineer, the machines are operated by “technicians” from whom 
only little mathematical knowledge is required, and who are instructed and 
trained in the same duties as they are employed. The duration of this theoret- 
ical and practical instruction and training varies with the countries and orga- 
nizations from 2 to 6 months. To be noted also, at least in the organizations 
large enough, is the specialized personnel, providing plotting data; control 
reports, plotting, drawing projections, field surveys before or after plotting. 
Finally the organizations which use aerial triangulation for obtaining part 
of the map control generally assign to this work special machines and operators 
who are often engineers or assistant engineers having theoretical ability much 
stronger than the operators assigned to tracing the maps. No further details of 
organization hours of work, etc. will be discussed except to note that certain 
services work teams in successive shifts as Italy for example, while in other 
services each operator has a machine at which he is the sole worker during 7 
or 8 hours per day. This is the case in France at the IGN. 
The foregoing information constitutes the pattern of organization but 
certain cases form exceptions to these general rules. Thus at the Swiss Federal 
Topographic Service, the team is composed of a draftsman and a topographer 
who may be an engineer. The cadastral map of Switzerland is surveyed in 
private photogrammetric offices of which the chief must be a licensed surveyor. 
At the Public Works Ministry of Belgium the operating personnel are 
recruited from secondary schools and do plotting as well as ground surveying. 
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