8. Construction of the Route Map on Scale 1:2,000,000
In the process of utilizing the dead-reckoning for the determination of the longitudes of the principal camps, the whole route had been provisionally plotted on to a scale of 1:500,000 direct from the field-books, on a series of sheets each comprising one section of the route. To these plottings of the actual route were now added the computed levels of all camps, the geographical features fixed by cross-bearings on either side of the route, and notes on the nature of the ground. The various sections thus provisionally mapped on 1: 500,000 were then reduced to the scale of 1:2,000,000, allowance being made for the small departures of the original plottings from the 1:500,000 scale as found by the latitude-observations, and the various sections so reduced were drawn in on the final map between the finally adopted positions of the principal camps. It was found practicable to show all the principal geographical features on the final scale, though many notes on the nature of the ground had perforce to be omitted in order not to overcrowd the map. These notes are however carefully preserved on the 1:500,000 manuscript sectional maps in the Desert Survey Office in Cairo, so as to be available for future reference, while the principal of them are incorporated in Hassanein Bey’s narrative of the expedition.
The main portion of the route, namely that from Jaghbub to Furawia, has been mapped entirely from Hassanein Bey’s journals and note-books. The portions of his route from Sollum to Jaghbub in the north, and from Furawia to El Obeid in the south, have been copied from the latest official survey maps of Egypt and the Sudan, as being more accurate than any route survey could be.
The fixing of the positions of El Harrash and Taj by Hassanein Bey’s observations has enabled the course of his former expedition to Kufra (with Mrs. Forbes) in 1920-21 to be delineated more accurately than was possible from the original records of that journey, which were unaccompanied by any astronomical observations; and the course of the former route, adjusted to newly determined positions, has been indicated on the new map by a dotted line.