4 — On the final testing of contours in air surveyed maps on large scale. 
  
The following proceeding can be applied for determining the maximum 
amount of the allowable planimetric divergency between the two runs of a con- 
tour line obtained by the first original plotting and the second control plotting. 
We will consider an infinitesimal tract of a generic contour line C, cal- 
ling L; its mean planimetric distance (at the fore-said tract) from the two adia- 
cent contour lines (the preceding contour line (C, and the following 
one C,) and « the angle of slope of the ground in the considered tract. 
In this case it is possible to demonstrate (1) that the divergency /; between 
the first run C", and the second run C"', of the contour line C, must correspond 
in the considered tract to the condition 
d _ 2,64 
L; E 
  
M [1] 
in which M is the mean plotting error of the contour line at given slope of the 
ground and at the considered map scale; E is the contour interval. 
Further, the contour line C”,, plotted for verification, obviously 
must not touch the adiacent contour lines C,, C, and also not overstep — on 
the one or on the other side — the strip formed by the latter two lines; therefore 
À c M 
Li E 
  
M < 1 [1] 
For the usual flying heights above the ground, the following values, ob- 
tained in a theoretic and experimental way (2), can ben attributed to M: 
For scale 1:2000 mu 
(usual flying height 2000 m) M; — T f 0.50 + 1,20 tg? x, [2] 
  
For scale 1:4000 
(usual flying height 3000 m) M, — T V 0,90 + 3,14 tg* « [2] 
1 
And furthermore we have, obviously: iga — — [3] 
i 
Let us now suppose, on the other side, that the contour interval E would 
have been chosen not only with regard to the scale and to the use to be made 
of the map, but also according to the medium slope of the ground in the con- 
sidered zone and let us apply the terms indicated in an other communication to 
(1) see A. Paroli — The mean error in plotting contours for air photogramme- 
tric mapping — in «Rivista del Catasto e dei Servizi Tecnici Erariali» — 
Rome, 1940. 
(2) see A. Paroli - The altimetric mean error in the aerophotogrammetric maps 
of the new Italian Cadastral Survey — Communication to the 5th Interna- 
tional Congress of Photogrammetry — Rome, 1938.