PHOTOGRAPHIC SURVEYING. 
123 
are, however, countries where this system cannot be carried out, such, 
for instance, as portions of South Africa, where the local attraction, owing 
to the presence of magnetic iron, varies so much that the compass is 
rendered useless for this purpose. A note should always be made in 
the field-book when this system has been adopted. 
Photographic Surveying. 
By J. Bridges Lee, m.a., e.g.s. 
Since the last edition of ‘ Hints to Travellers J was published, numbers of 
people in different parts of the world have been working at the practical 
development of “ Photographic Surveying.” A vast amount of most 
excellent photographic survey work has been done in Canada and other 
countries. Text-books specially devoted to the subject have been 
published and instrumental appliances have been very much improved, 
and surveying by photography is now one of the recognised means by 
which reliable maps may be made. 
Practical Advantages for Travellers . 
For travellers especially the method has certainly great advantages. 
For example:— 
1. Anyone who is compelled by circumstances to travel quickly may 
be able to find time and opportunity to expose a few plates, though he 
qould not find time to stop many hours or days to make and record a 
large number of observations at selected station points. 
2. Good photographs commonly contain records of an amount of detail 
which could not possibly be plotted from direct observations in the field 
without the expenditure of a vast amount of time. 
3. The traveller is not so exclusively dependent upon himself or his 
immediate assistants for the accuracy and completeness of his work as he 
would be if he employed exclusively any of the better-known methods. 
He can invoke the aid of skilled photo-topographers at home, and he need 
do little more himself than to select and fix his station points with care 
and expose his plates with judgment. 
