402 SECTIONAL TRANSACTIONS.—E. 
Monday, September 9. 
JoINT SYMPOSIUM AND DiscussI0N with Section C (Geology), on Denudation 
chronology (Section C Room, 10.0). (See under Section C, p. 374.) 
AFTERNOON. 
Excursion to site of Hockham Mere, Breckland and Peddlar’s Way. 
Conducted by Mr. J. E. G. Mosby (2.0). 
Tuesday, September 10. 
Capt. A. W. Heap.—Aeronautical maps (10.0). 
1. Introductory. 
Maps were originally produced for the use of soldiers, later the general 
public began to use them and to demand special types of maps for special 
purposes. ‘The airman now requires special maps for his use. 
2. The Problem. 
(a) Scale. 
Deciding factors : Speed of flight. Map-carrying capacity 
of the aeroplane. Amount of detail of use to the airman. 
These factors conflict with one another. The present 
trend of opinion favours a scale of 1/500,000 for general 
navigational purposes. 
(b) Projection. ; 
Requirements are: Accurate bearings. True shape of 
topography. ‘True scale. 
These ideals are not attainable on any one map. Choice 
of projection must depend on the shape and latitude of the 
country mapped and on neighbouring countries. 
(c) Detail. 
In all cases hill features and heights are of importance 
and usually water. Relative importance of other detail 
must vary with the country being mapped and with the 
purpose and scale of the map. 
3. Conclusion. 
The ideal method of designing any aeronautical map is to survey the 
ground from the air. This is usually impracticable. Aeronautical maps 
are still very much in their infancy ; the preceding remarks therefore show 
the present trend of thought and do not pretend to be a statement of final 
conclusions. 
Specimen aeronautical maps passed round during the discussion. 
Lieut. M. O. CoLiins.—The revision of large scale Ordnance Survey 
maps (10.45). 
The large scale revision surveys are of peculiar interest to this country, 
as it is the only one where such surveys have been in existence for upwards 
of fifty years. "The system of carrying out these surveys is in itself a develop- 
ment of the methods employed in the original work. ‘The history of the 
various revisions is of interest, showing as it does both the present position 
and the possibilities of the future. The future possibilities may be con- 
