Figure 417.—Forward overlap.
Figure 4-18.—Effect on scale when photographing over rough
terrain.
missed. Since only the central portion of each
photograph is used in a mosaic map, each successive
strip must overlap the preceding strip. This overlapping
of strips is called SIDE LAP. Side lap for mosaic maps
is usually 40 percent (fig. 4-19).
Since each flight strip is overlapped 40 percent,
only 60 percent of sideways usable area remains on
each negative. To find the amount of usable
ground-gained sideways, multiply the ground coverage
by 0.60. For example, when the ground coverage is
9,000 feet, the usable ground-gained sideways (GGS)
is 5,400 feet (9,000
0.60 = 5,400).
The shorter dimension of the negative is always
used for the GGF. This is to limit the number of flight
lines to as few as possible. This helps to eliminate the
Figure 419.—Side lap.
4-21
