On the final testing of contours in air surveyed maps on large scale, 
    
  
  
  
  
  
  
  
TABLE li 
Scale 1 : 4000 (flying height above the ground 3000 m) 
Contour Interval Contour Interval Contour Interval Contour Interval 
E = 4m E = 8m E — 16 m E = 32m 
L l L; l Lol. A, L, l 
mm mm mm mm mm mm mm mm 
20 12,5 6 6 1,5 6 1 
18 11,5 5 5 1,5 5 1 
16 10 4 5 4 1,5 4 1 
14 9 3 1,5 3 1,5 3 1 
12 7,9 
10 6,5 
8 5 
6 4 
5 3,5 
4 3 | 
3 2 | | 
  
  
  
  
  
  
  
  
  
  
  
As results evident, the use of tables is the simplest one and it is neither 
necessary to know the slope of the ground nor to proceed to any calculation. 
It is sufficient to measure graphically — at the various corresponding points — 
the divergency between the second plotting of the contour line and its first tra- 
cing; further the medium distance 7; between the same contour line and the two 
adiacent ones is to be measured. The knowledge of this distance is necessary, in 
order to can read off the allowable error /; from the table established for the 
relative scale and flying height. 
The above described proceeding has been applied in Italy — together 
with that consisting of the survey of profiles of the ground — for the verification 
of contours contained in the air surveyed maps of the Italian Cadastral Survey. 
Besides the advantages of easy application and celerity, it permits to verify large 
groups of contour lines with relatively low expenses as no measurements on the 
ground are needed. 
The limits of error indicated in the two tables are referred to verifica- 
tions to be carried out during the plotting operation, as in this case the orienta- 
tion of photographs is varied between the first plotting and the following con- 
trol plotting. 
Therefore, if the second plotting is carried out after some time for the 
final testing of the map, setting of the pairs of photographs in the plotting ap- 
paratus must be repeated and it will be necessary, in such a case, to take into 
acount also the (doubtless very little) differencies between their new orientation 
and the former one they had during the first plotting. This can be done adequa- 
tely increasing the maximum errors /; indicated in the two tables. 
It would be possible, of course, to apply an analogous proceeding also 
for testing of the accuracy of planimetry. However, in this case the verification 
would be less precise as the fidelity of planimetry not only depends on the degree 
of accuracy of the plotting, but is also and mainly connected with the accuracy