May, 1960 Commission IV 187 
for some 820,000 square miles in northern Canada. This photography provided the 
horizontal information for the control of slotted-templet assemblies used in the com- 
pilation of the 1:250,000 mapping. 
In 1958, the Shoran-controlled photography program for horizontal control of 
1:250,000 mapping was discontinued. Although this was a satisfactory method in terms 
of the required ground survey effort, the problems, as the work progressed further into 
the Arctic regions, became increasingly difficult because of the high costs involved. 
Basically, the Shoran program was most successful in terms of economy when applied 
to very large areas. The heavy costs entailed in launching the program may then 
be defrayable over the large area. As the work progressed northward the uncertain 
weather conditions and relatively short working seasons together with the great 
distances involved made it more difficult to ensure reasonable returns from the high 
initial costs required to launch a Shoran project. 
In 1959, ground survey replaced the Shoran as a means of providing horizontal 
control for 1:250,000 in the Arctic. New developments made this replacement possible: 
the use of the radar profile recorder on flight missions, introduction of tellurometer and 
helicopter team in the field survey parties, and of the Jeri analog computer into the 
compilation work. 
The tellurometer had been quite successfully employed in southern Canada for 
traverse work and the helicopter was a satisfactory answer to the surveyor's transpor- 
tation in the field. It was, however, necessary to devise some method of laying much 
larger slotted-template assemblies, using perimeter control and enclosing larger areas, 
before field costs could be reduced below Shoran costs. The Jeri analog computer 
was used to obtain a better adjustment of the template assemblies and permitted the 
field surveys to enclose with perimeter control a larger area, roughly 140 miles square. 
The combination has made it possible to establish horizontal control more cheaply 
and with a much higher certainty of completing a given area, since ground survey is 
less dependent on the weather than airborne Shoran operations. 
The airborne radar profile has been used very extensively in the northern latitudes 
of Canada to obtain vertical information for 1:250,000 mapping. When possible, the 
profiles are taken simultaneously with the survey photography. In the event that the 
survey photography is already flown, or if for some other reason the profile cannot 
be taken with the survey photography, the profiles are flown transversely across the 
survey photography flight lines, spaced at intervals suitable for subsequent photo- 
grammetric bridging. Ground survey level lines are run to supply datum for the 
adjustment of the profiles, and are spaced so that the length between level control is 
of the order of 100 miles. The dense pattern of lakes in the northern areas makes the 
identification of position between the profile and the positioning photography com- 
paratively easy and reasonably precise, so that the tying of the profiles togecher or to 
ground control can be fairly reliable, with accuracy of heights obtained from the 
profile falling into a range of — 15 to — 20 feet on the average. 
Topographical mapping at scales of 1:50,000 and 1:25,000 is carried out by con- 
ventional methods. Precision plotters perform the aerotriangulation bridging and 
stereo-templet assemblies are used to adjust a block of strips. Compilation is usually 
made with the Kelsh, Balplex, Multiplex or similar type of plotter. 
There has been a definite trend towards the automatic recording of instrument 
readings and the solving of the horizontal adjustment of a block of strips by the 
electronic computer. Although this is not in general overall use, the indications are 
that this application will continue to grow. Such work already done with this approach 
has given promise of increased accuracy and reduced cost. New techniques for this 
and for an analytical solution have been developed by the Photogrammetric Section of 
the National Research Council of Canada.