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strengthening supplemental control on the survey project, photographic targets 
are placed on the ground centered by semi-permanent station markers, consist- 
ing of a tack in a wooden stake driven into the ground, in open, unobscured, 
and flat ground areas, on crests, in saddles, and on uniform slopes. Targets 
are also centered on property corners-and lines, wherever these will not 
appear clearly defined on the aerial photographs as images of fences or vege- 
tation rows along fences, walls, streams, or other natural boundary indicators. 
Moreover, photographic targets are placed on the ground centered on any fea- 
tures for which correct designation and exact position will be required and 
which will not be readily identifiable on the photographs, such as underground 
utilities, centerline and stationing points of existing roads, and section 
corners of land surveys. 
The preferred interval of placing photographic targets centered by perma- 
nent station markers along the lengthwise direction of the route survey is not 
more than one mile (1.6 kilometers) in rural areas and one-half or one-quarter 
mile (0.8 or 0.4 kilometer) in urban areas. Their placement on such markers 
is as near the center of the route as possible, and seldom is their lateral 
placement more than 200 feet (60 meters) from the center. The interval of 
placing photographic targets centered by semi-permanent station markers along 
the lengthwise direction of route and normal to the center of route is given 
in table 2; such placings are staggered alternately in the right one-half and 
the left one-half of the route photography band, and, wherever possible, 
placement on the center of that band is avoided. 
Table 2. — Interval of placing photographic 
targets on semi-permanent station markers 
  
  
  
  
  
  
  
  
  
  
Feet Meters 
Positioning Number of times photog- . Fraction of denominator 
raphy scale in feet to of representative frac- 
one inch tion expressing photog- 
raphy scale 
desirable maximum desirable maximum 
Lengthwise not to not to not to not to 
direction exceed 2 exceed 1.8 exceed 1/20] exceed 1.8 
of route times the times the 
desirable desirable 
minimum maximum minimum maximum 
Normal to not less not much not less not much 
center of than 3 more than than 1/13 more than 
route 5 1/8 
  
  
  
The shapes of the targets are either an ordinary cross or a diamond- 
centered cross. The spread of the legs of the cross in feet is 1/50 the scale 
of photography in feet to one inch, and in meters is 1/2,000 the denominator of 
representative fraction expressing photography scale. The width of the legs in 
inches is 1/60 the scale of photography in feet to one inch, and in centimeters 
is 1/300 the denominator of representative fraction expressing such scale. The 
side of the central diamond in feet is 1/150 the scale of photography in feet 
to one inch, and in meters is 1/6,000 the denominator of representative frac- 
tion expressing photography scale. As to color, the central one-third of each 
cross-type target and the diamond center of the other type target is black or 
dark red where the ground has light color tone. Where the ground is dark or 
covered with short green grass, the central portion need not be covered. Each