GVII-50 
PHOTOGRAMMETRIC ENGINEERING 
mapping of either the planimetric or topographic type, or both. In the first three high 
way engineering stages, this mapping is reconnaissance in character—seldom done pre 
cisely as in the subsequent stages. 
“Step five is classification. All features of importance that have been identified, 
interpreted, numbered and measured, are classified according to the effect or influence 
they will have on the making of decisions and on preparing plans. In this step lies one of 
the greatest needs for the many specialists. Each specialist is concerned by degree or 
magnitude with certain types of features and has no concern about others. 
“Four examples are: By use of sequentially taken stereoscopic aerial photographs 
and other data, traffic engineers will classify the principal traffic arteries, the traffic 
“bottle-necks,” vehicles by type and number, and where traffic came from (origin) and 
is going (destination). Rights-of-way experts (land appraisers) will classify the land by 
type and intensity of use, and value it in terms of cost for a highway right-of-way. Soils 
engineers will classify the topographic area by soil types and their condition, or by the 
indicators of soil types and their condition as land form (including geologic structure), 
ground slope, drainage pattern, position, color tone, vegetation, and types of land use. 
Drainage engineers will do their classification according to the physiographic region, by 
drainage area, channel length and slope, and at bridge sites by profile and cross sections 
of channel and flood plain for considerable distances both upstream and downstream 
from each possible site. 
“The sixth step is evaluation. While this is akin to classification it is also different, 
especially in degree or quality. Evaluation is the process of ascertaining the degree of 
importance of the classified features. It is easy to realize at this point why evaluation is 
essential. It is actually a process of elimination by degree after selection by classifica 
tion. A highway engineering problem could not be solved at reasonable cost in terms of 
both time and money, unless the features of influence are chosen, evaluated, and the un 
important eliminated. Evaluation is actually the determination of the weight that should 
be given each feature in the decisions that must be made. 
“The seventh step is the decision—the utilization of all qualitative and quantitative 
features obtained, classified and evaluated which have influence on results. Here again 
each specialist does his part in cooperation with all others concerned. Team work is 
strength at this point. 
“Step eight is preparation of a description of the results of the work of all contribu 
tors. The description is usually in one of three forms or any combination. The first is of 
words (a report); the second is a pictorial presentation (a perspective drawing or nota 
tions on aerial phtotographs, either of the oblique or vertical type, or both); and the 
third is orthographic plans of the map, profile and cross section type. The degree of re 
finement and accuracy of the description is gauged according to the purpose and the 
highway engineering stage in which prepared and used. 
“Once step eight has been completed for one stage of the highway engineering cycle, 
the specialists are prepared to begin work on the next stage. Progressively they can, in 
that manner, attain the ultimate in satisfactory results. No factor of importance need be 
overlooked. Moreover, they have prepared themselves to do the best work possible 
from stage to stage.” 
PHOTOGRAPHIC INTERPRETATION IN RAILWAY SURVEYING: 
Considerable railway surveying by means of aerial photography was per 
formed during this reporting period in England. The requirement was primarily 
photogrammetric, and resulted in the preparation of large-scale railway plans. 
Equipment used included in some cases Kelsh plotters, as well as such first- 
order equipment as the Wild Stereoautograph and the Zeiss Stereoplanigraph. 
With respect to the interpretation aspects, the production by both types of 
machine, of railway plans at a scale of 1:480 has called for very precise inter 
pretation of engineering detail, although the survey companies concerned insist 
that elaborate ground checking of interpretation is essential, possibly more so in 
the case of railway plans than in the case of factory and site plans at the com-