521
On the one hand it was obvious that the planning of the mine, the
railway and the harbour must be based on aerial photography and
mapping. On the other hand it was clear that the existing map of
Liberia, i. e. the American aerial mosaic based on aerial photographs
taken in 1952——53, could be used only for the first outlines. The lack
of a vertical control system was a vital point.
For time-saving reasons it was desirable, however, to start the plann
ing by means of the already existing American aerial material. Thus,
at the end of 1956 the first map of the Nimba Area was prepared by
means of photographs delivered by the US Air Force in Washington.
The vertical control points required were furnished by the Lamco
geologists at Nimba by means of a barometric measurements. At the
same time the staking of the railway line, made in Stockholm as an
interpretation study, was pursued in a forced way. This preliminary
proposal of the railway line required an up-to-date photography for
Lamco.
Thus, the first aerial photography was carried out in 1957 and the
second one in 1960.
In 1958, when it was decided that a more accurate mapping had to
be carried out it was considered necessary to establish geodetic net
works of such an order that an aerial mapping would give the accuracy
needed even for the large-scale maps in question.
According to these plans, a first order geodetic network, called the
Nimba Geodetic Network, was planned including the total area of the
Nimba Concession Area and surroundings. It was carried out as a
trilateration in combination with a common triangulation.
The network consisted of six (6) first order points and twenty-
two (22) second order points.
3.1 Connection of the Network
The next step was to connect the local Nimba network with the offi
cial map of Liberia, i. e. to the co-ordinate system of the American
Aerial Mosaic. The primary reason for that was the requirement to get
the mapping areas of Nimba and Buchanan locally connected with the
surroundings for any measuring extended out of this area. It was also
considered desirable to connect the areas due to the levelling system of
the railway line.
When the connection problem was scrutinized it proved to be a
complicated task.
It was obvious that only a few places identified on the American
mosaics could be recognized on the Lamco photographs of 1957. Since
the American aerial photography in 1952—53, taken from an altitude
of 6,000 m, the changes have been so far-reaching that the larger towns
only could be recognized on the photographs of 1957.
From this point of view, the only features well defined in the both