National Institute of Informatics - Digital Silk Road Project
Digital Archive of Toyo Bunko Rare Books

journey in 1907-08 along the Chinese high road from Kāshgar to Kan-chou ; ¹ the latitudes
observed by Dr. Sven Hedin along the Tārim river and in the Lop depression ; ² Captain
H. H. P. Deasy's extensive triangulation work on the Chinese Pāmirs and in the K'un-lun
range east of Khotan ; ³ the triangulation done on the Kara-koram in connection with
Sir F. De Filippi's expedition. ⁴

Co-ordination of
successive surveys.
Apart from the use of certain latitude and longitude determinations just referred to,
the topography of the maps now published is based solely on the results
of our surveys. Special care has been taken throughout correctly to
coordinate these results where the same or closely adjoining areas were
surveyed on successive journeys. In order to assure greater accuracy in details reference was
also made throughout to the original plane-table sheets in the case of ground already
represented in the maps illustrating the first two expeditions. This has proved of particular
advantage for the delineation of mountainous ground surveyed on the second journey, since
the hachuring on the previous maps did but inadequate justice to the horizontal 'form lines'
shown on the original plane-tables.

Use of descriptive
records.
Where the same route was followed on more than one journey preference was given
to the representation of the ground by the later survey, if done under
my direct supervision or on a larger scale. When revising the 'fair
drawings' of the map sheets I endeavoured to check, and, if necessary,
to supplement topographical details by reference to the descriptive records I had kept of all
routes personally followed. This task was greatly facilitated wherever the preceding pre-
paration of my Detailed Reports had obliged me to make a thorough study of these diary
records. Reference to them proved particularly useful in respect of minor features which the
original plane-tables of the first and second journeys did not sufficiently differentiate, e.g., as
regards the various types of desert vegetation (tamarisk-cones, reed beds, etc., living or
dead), and the permanence of water in stream beds, etc. ⁵

Altitude records.
Apart from those determined by triangulation, height records were obtained on all
three journeys by aneroid barometer and hypsometer observations. On
the second and third journeys the aneroid barometers were controlled
by simultaneous readings of a mountain mercurial barometer whenever
time and conditions permitted. Height records obtained by mercurial barometer were given
preference for entry in the maps and intermediate aneroid readings adjusted to those of the
mercurial barometer readings. The methods used for the computation of barometric heights
have been indicated in Appendix B, supplied by the kindness of Dr. J. de Graaff Hunter,
in charge of the Computing Office. Comparison with the mercurial barometer records proved
that the aneroids preserved a very uniform rate of accuracy throughout the third journey.
As their readings were also found to agree more closely with the heights deduced from verti-
cal observations with the theodolite in the course of triangulation they were adopted in
preference to the hypsometrical heights. The latter were, however, used where no barometri-
cal records were available.

Hill-shading by
contours.
On the second and third journeys extensive use was made of the clinometer to fix the
approximate elevation of points intersected from positions of which the
heights were barometrically determined. The help derived from these
additional data as well as from the 'form lines' of the plane-tables
and from photographic records, such as the numerous photo-theodolite panoramas I secured
on the first journey, led to the hill-shading of the new maps being given the form of regular
contouring, with approximate contour intervals of 250 feet. Where trigonometrically deter-
mined heights were available, these have been used as the basis for levels, barometric and
clinometric heights serving the same purpose elsewhere.