630 REPORT—1904. 
second order, and a framework of the third order; and so on, A perfect map is, in 
fact, formed of points of six orders of accuracy, and it is approximately true that the 
accuracy of direction of any line joining adjacent points of the same order will 
vary directly as the length. The control of the ‘ relief,’ the vertical framework, is 
similar; here we have points of five orders of accuracy, from the primary levelling 
to the freehand lines joining the contour points. 
6. In forming this structure only one alteration of principle has of recent 
years been attempted—namely, the use of photography for topographical purposes. 
It is, however, a method which has a very limited field of usefulness. It has been 
successfully used in Canada in very special circumstances, but ordinarily the 
topographer working on customary lines will be quite prepared to prove the 
superiority of the recognised methods in the matters of accuracy, rapidity, and 
cost. An extension of an old principle, recently employed with effect on the Gold 
Coast, is described below. 
7. The following is a brief description of the methods (in use or proposed) of 
forming topographical maps in the British Empire :— 
(1) The United Kingdom.—The small-scale maps of the United Kingdom are 
formed by reduction from the 6-inch map, which itself, so far as detail is con- 
cerned, is reduced from the g455. The resulting map is of the highest possible 
accuracy. Of course this system cannot be employed as a general rule on account 
of the expense, and would not have been used at home were it not that large-scale 
maps (cadastral maps) are a necessity. 
(2) India.—Vast areas in india have been topographically surveyed by tri- 
angulation and plane-tabling. It is especially interesting to study this system at 
work during an expedition. The recent operations in China afford a noteworthy 
example; the Survey of India party surveyed about 17,000 square miles on the 
3-inch scale. Similar work is now going on in Tibet. 
(3) The Gold Coast.—In the survey of this territory we find, for the first time, 
‘long traverses.’ The expense of triangulation in such dense forest would be pro- 
hibitive. Hence the country is being divided up by long primary traverses, and 
at the junction-points of these traverses latitudes are observed having an apparent 
probable error of 0-2’, It is easy to show that on account of ‘local attraction’ it 
is no use multiplying the number of these latitudes. The average length of a 
traverse is about 70 miles! Between these traverses minor and compass 
traverses are run. Here we have points of the second and lower orders. 
(4) South Africa.—Whenever the systematic survey of South Africa is com- 
menced it will start under most fayourable conditions.- First because, thanks to 
Sir David Gill and Colonel Morris, the geodetic triangulation of the Cape Colony 
and Natal is complete, and that of the other colonies is progressing. Secondly, 
the country is for the most part very suitable for a plane-table survey. The 
accuracy and economy of plane-tabling are at their greatest in an open country 
provided with scattered hills, and much of South Africa answers to this descrip- 
tion. 
(5) Canada.—At the request of the Dominion Government, Major Hills, the 
head of the Topographical Section of the War Office, drew up a report, after con- 
sultation in Canada, which forms a valuable scheme for the topographical survey 
of this vast territory, a scheme which it is much to be hoped will be carried out. 
It comprises, in brief :— 
i, A geodetic arc from the St. Lawrence to Vancouver. 
ii, Secondary chains depending on this. 
ii. A topographical triangulation covering the interstices with a network. 
y. Topography (to be carried out mainly by plane-tabling) ; the standard scale 
to be 4 inch to 1 mile, 
1 Two traverses were lately carried out independently between points 140 miles 
apart, the results showing a difference of 25 feet only at the terminal point. 
