4 
each parcel of the land which will be taken for the right-of-way; the 
ease with which ingress and egress can be made to and from the new 
highway; the sight distances achievable; and how well the highway can 
be made an integral part of the entire landscape. 
Photogrammetrically compiled maps and photographic mosaics 
utilized and augmented by stereoscopic examination of aerial photo- 
graphs can be small in scale, such as from 1:10,000 or 1:12,000 to 
1:48,000 or 1:50,000. The larger scales are used in areas of intense 
land use, and the smaller scales are used where topography is rugged 
and land use nil. The accuracy of these maps is commensurate with 
their scale, but need not exceed what is feasibly achievable by the 
elemental photogrammetric use of aerial photographs using basic 
control survey measurements made on the ground to satisfy third order 
accuracy requirements of 1:5,000 for the horizontal and in the vertical 
of 0.05 of a foot times the square root of the length of the level 
circuit measured in miles, or 0.012 of a meter times the square root 
of the length of the level circuit in kilometers. 
Comparison of Feasible Routes to Select a Route for Survey. 
Once the feasible routes are determined, they must be compared 
in sufficient detail to ascertain which of the alternatives should be 
selected for the highway. Comparisons on a relative basis are essen- 
tial rather than by absoluteness of position or exactness in physical 
dimensions. It is more important to determine the gradients; the 
curvature; cross sections; volumes of excavation and embankment, and 
other construction quantities, including drainage, bridges, culverts, 
retaining walls, and so forth; plus the sight distances; the rise and 
fall; the ease of constructing access and exit ramps, or intersections 
at grade where controlled access is not to be applied; the cost of 
rights-of-way, the costs of construction and maintenance, the costs 
of vehicle operation on the highway; and, significantly, the service 
which the highway can provide to the motor vehicles which will be 
using it, plus service to users of bordering lands which will generate 
vehicle traffic. Accordingly, relative rather than absolute, measure- 
ments in X, Y, and Z will suffice for determining the characteristics 
of vehicle movement and their positional relationships on the highway. 
Topographic map scales of from 1:2,400 or 1:2,500 to 1:5,800 or 
1:5,000 are usually adequate, with the larger scale being used in urban 
areas and the smaller scale in rural areas, and a scale as small as 
1:9,600 or 1:10,000 being used in mountainous regions. Contour inter- 
val ranges from 5 feet to 25 feet or 1 meter to 10 meters. Precision 
in the maps should be greater in this stage, of course, than in the 
preceding stages. Actually, the photogrammetric measuring and mapping 
accuracy is comparable to what can be achieved in photogrammetric 
compilation using supplemental control of third order accuracy, meaning 
1:5,000 in the horizontal and in the vertical of 0.05 of a foot times 
the square root of the length in miles, or 0.012 of a meter times the 
square root of the length in kilometers, of the level circuits. Only 
the basic control throughout metropolitan areas, where land use is 
intense and land values are high as compared to values in rural areas, 
should have accuracies exceeding those mentioned. In such cases, the 
error in basic control should not exceed one-half the errors expressed 
previously for other areas.