(412) 
subsequently reduced to the 1:50,000 publication scale. 
By the time the provisional edition showing only the planimetry is issued, 
the contouring undertaken in multiplex may be only half completed. Work on 
the contouring proceeds as fast as possible, and when complete the contours are 
superimposed on the detail and the final edition of the map is prepared. 
The Directorate has a large amount of British Williamson Multiplex used 
principally for the delineation of the contours. 
Plan control for the multiplex is from the slotted template assembly and 
height control is normally from aneroid spot heights obtained in the field. 
Most of the flying has been undertaken for the Directorate by the Royal 
Air Force who use Gee H radar for navigation. The radar is frequently put to 
good use as partial control for the photography where ground control is sparse. 
Recently an increasing amount of our photography is being contracted out to 
private companies. 
The Directorate do not consider any of their current methods as rigid or 
fixed and are continually seeking to improve them and to adapt them to con- 
ditions as circumstances and economy may rule. The important consideration is 
always to speed up production without loss of accuracy. 
Williamson Multiplex equipment used by the Directorate has been continu- 
ally improving in quality and performance and has given very good service. An 
interesting development is the prototype design of a three projector bar designed 
to deal with awkward photographs, such as the end join of two strips not flown 
on exactly the same alignment. There are two normal projectors, but a third 
projector is made so that it can be rotated in any direction about the node of 
the central projector. Adjustment of all three projectors is then possible by tip, 
tilt and swing only and without the necessity of employing b, or b; it being 
well known that when photography gets badly out of alignment adjusting 
systems using by and b, become excessively difficult to undertake. 
The Directorate also has a Wild A5 which is put to excellent use for large 
scale town plans and highly developed islands, and shortly hope to have a 
stereoplanigraph in operation. 
One of the British Commercial companies also possess a number of Wild 
plotting machines which they put to very excellent use. 
8. Conclusion. 
The point I have tried to make in this paper is that in Great Britain, the 
first consideration is not to provide a map at a specified scale or accuracy, but 
to provide mapping that will adequately serve the purposes for which it is 
required, bearing in mind long term as well as short term requirements. 
The scale and accuracy specification of any particular map made at any 
particular time is decided only after the most careful consideration of this over- 
riding requirement. 
In looking at the survey problem in this way, which I believe is the only 
right way, the British have not found so wide an application for precision 
plotting machines as has been found in several other European countries. 
Precision plotting machines are used for some work and also a large number 
of other techniques. Nor do I think we have been much slower than other 
countries in seeing the many advantages of the air photograph and in developing 
photogrammetric methods.