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the finer details, F or this reason planimetrie measurements can not 
always he avoided, 
II 
EXECUTION OP THE WORK 
1. - GENERAL 
The controlled mosaic c.overs a stretch of the Zambe 
zi River from the Lupata Gorge to its mouth, including most of the 
delta. ^his stretch is approximately 370 Kms. long and spans, in its 
minimum width, from bank to bank. The total ground area covered by 
the controlled mosaic is approximately 1.466.700 acres. 
On account of the large volume of the work involved^ 
its peculiarities and shortcomings, various problems and difficulties 
had to be overcome and solved on a practical and economic basis. 
Although the solutions found could net possibly always 
be the best, they allowed nevertheless, the execution of the job 
within the prescribed time and with results considered to be accep 
table . 
The following is a short description of how the work 
was carried out, with special emphasis on the most interesting and 
significant steps. 
2. - AERIAL PHOTCGRAPHY 
The scale of the existing aerial photography - 1/50,000 
- and the flight direction - across the river- would obviously not 
permit the elaboration of the controlled mosaic at the required scale 
of 1/10.000. 
Should the photo coverage be carried out directly on 
the scale of the mosaic, many of the photographs would cover mostly 
water. This would consequently raise eerious problems when choosing 
the tie and carry over points for the triangulation. 
It was, thus, decided to make the new coverage at.a scale 
1/20.000 and later enlarge it twice to the scale of the mosaic. As 
a consequence of this the photographs had to be taken only under 
the best light conditions and with totally clear skies. 
The number of favourable days in the area is small? in 
this respect the 1/20.000 photo scale reduced considerably the cost 
and time required for the aerial coverage and, therefore, those of 
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