2] 
3 
4 
/ 
Fig. 17 
indicated by the dashed line. A profile, as shown on Fig. 17, indicates that 
line 2 has an CO error. The proper adjustment is indicated by the dashed line. 
6. EXTENSION OF HORIZONTAL CONTROL 
On the projects in Nigeria, Gabon, and Canada, the horizontal 
control was extended by employing the well-known stereo-template method. The 
stereo templates were prepared at the same time as the vertical bridging. 
Presently, we are experimenting with an analytical method of adjustment of 
independent stereo models in a block. The method of "A Simultaneous Section 
Adjustment for Small Computers," by J. J. Therrien, and the method of "Three- 
Dimensional Transformation of Higher Degrees," by E. M. Mikhail, appear to be 
the most promising for this purpose. 
7. ACCURACY OF THE MAPPING SYSTEM 
The mapping system described in the previous paragraphs was 
successfully employed in Africa and Canada. On these projects almost 5,000 
vertical aerial photographs were triangulated. The experience gained on these 
projects permits an evaluation of its economy and accuracy under widely diverse 
atmospheric and climatic conditions. 
7.1 Experience in Nigeria 
To determine the accuracy of this method under the operating 
conditions likely to be encountered in the broad project, a test area was 
established in Nigeria in the fall of 1961. This test area measured approxi 
mately 34 x 34 miles (55 x 55 kms). It was covered by nine flight lines of 
photography averaging 15 stereo models each. Ground control was established at 
both ends of each line. In addition, 97 vertical points were established