the maximum flight height above the lowest elevation by an amount equal to 
60 percent of the maximum relief height. Under such conditions and in the case 
considered, the optimum flight height at which the photographs would be taken 
is 1,500 feet (457 meters) above a plane passing through an elevation 60 per- 
cent of the relief height higher than the lowest elevation in the stereoscopic 
area. With the instrument being considered, this optimum flight height will 
permit mapping at a manuscript scale of 50 feet to one inch (1:600). A flight 
height of 2,660 feet (811 meters) above the lowest elevation would provide an 
optimum flight height of 2,400 feet (732 meters) and permit mapping at a manu- 
script scale of 80 feet to one inch (1:960), or in the metric System mapping 
at a scale of 1:1,000. Consequently, wherever the actual relief height to 
flight height ratio in the area of photography and mapping is less than listed 
in table 5, this ratio causes no difficulty in use of any of the instruments. 
It is only in large scale mapping for engineering purposes and wherever the 
relief demands it that this ratio must be considered and the scale of mapping 
governed thereby. 
Table 5. — Relief height to flight height ratios of 
some double projection photogrammetric instruments 
  
  
Photography 
Projection Focal Length h/H 
Instrument Ratio* (in.) Ratio 
Bausch & Lomb Multiplex 2.4:1 6 0.36 
Bausch & Lomb Balplex (525) 3.4: 6 0.28 
Kelsh Stereoplotter 4:1 8.25 0.25 
Kelsh Stereoplotter 5:1 8.25 0.21 
Kelsh Stereoplotter 5:1 6 0.25 
Bausch & Lomb Balplex (760) 5:1 6 0.25 
Nistri Photocartograph 5:1 6 0.25 
Kelsh Stereoplotter 7:1 6 0.22 
Nistri Photocartograph 7:1 6 0.22 
  
  
  
  
  
  
  
*The projection ratio is the number of times the stereoscopic model scale is 
larger, at the optimum projection distance of the instrument, than the scale 
of the vertical photography. 
Accuracy and completeness tests of maps 
Whenever maps are used without knowledge of their quality and accuracy, 
there exists the possibility that their ultimate actual costs will be much more 
than their initial costs of photography, ground control surveys, and compi- 
lation. If the maps prove to be deficient in completeness and accuracy, there 
will inevitably be added costs directly attributable to frustrations occurring 
from their use; coping with their errors and inadequacies as they are discov- 
ered during use; and having to perform, at a later time, such additional work, 
as necessary, to adjust for the effects thereof. Whenever these effects are 
not discovered and corrected before the design, and are actually not known 
until after the location survey has been made and highway construction is to 
be started or is underway, the added costs include costs resulting from work 
required to make needed revisions in the design and to prepare and issue change 
orders and extra work orders, costs of delays in construction while the pre- 
ceding work is being accomplished, and the costs of all increases in construc- 
tion quantities caused by the maps. Consequently, all maps should be tested to 
ascertain their qualities. Rejection of maps, however, can be made only on the 
basis of noncompliance with stipulations prestated in the form of appropriate 
specifications before the mapping is undertaken.