i. a. a large side overlap (56 %), which implies a good view; each 
stereo-model covers a little more than two map sheets, which provides for 
practical use of the stereoautograph, etc. 
The thumb-rule that the standard error of coordinates amounts to 
0.1 9, of the flying altitude and of elevation to 0.15 %, gives standard 
errors (0.06 metres and 0.09 metres) which well satisfy the demands. 
Film used 
In order to increase the stereooperator's possibilities of seeing and 
identifying small details, and thereby reduce the expensive field work, 
the decision was made to carry out the aerial photography with colour 
film (Kodak Ektachrome). 
Experience in Sweden of the use of colour film for large scale mapping 
was not very extensive, but tests that had been carried out had proved 
that the photograph is likely to be better than with panchromatic ma- 
terial. As regards accuracy, the results of the tests do not discourage the 
use of colour film. Colour film produced on an acetate base was used as 
this was the only type then available in Sweden. 
Control points 
Within the Community of Huddinge there already exist triangulation 
nets, traverse nets and level nets. Certain traverse stations were of an old 
date, so there was reason to suppose that a number of points were lost 
or that the marking of the points would be incomplete. In order to 
investigate this as well as the suitability of the remaining points as con- 
trol points for the stereo work, a field inspection of all traverse stations 
registered at the City Engineer Office was carried out. 
With this inspection as a basis a plan was made for the measuring of 
control points. This was done according to the rule that each map sheet 
in the scale 1:400 should be provided with six control points. (See 
picture No. 1). As far as possible, use was to be made of existing traverse 
stations. 
For the control points, coordinates as well as elevations had to be 
determined. As tolerance a standard error of 0.05 metres was decided 
u pon . 
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