WORKING GROUP 9 
BRINK 
505 
to quarry where it occurred in sufficient thickness or concentration, an attempt 
is made to distinguish between economical and uneconomical occurrences of 
the same material as two separate mapping units. 
Having thus selected the mapping units, the airphotos are examined under 
the stereoscope to ascertain which indicators could be used for the delineation 
of each mapping unit. The indicators which have been found to be of use for 
purposes of delineation are landform, drainage pattern, grey tone, surface 
texture and natural vegetation - in general order of usefulness. In rare cases it 
has been found that a particular mapping unit cannot be directly distinguished 
in the stereo-model: in such cases the unit is either disregarded entirely if it 
concerns a material which is of no particular significance for the highway con 
struction, or else it has to be delineated by resorting to grid borings in the field. 
Delineation and field checking, with further boring or digging where nec 
essary, are then carried out concurrently for the whole of the proposed route, 
and up to two or three miles on either side of the proposed highway. 
Method of presentation 
Having completed the delineation of the individual photographs, the map is 
compiled by whatever photogrammetric means is most appropriate under the 
particular circumstances. The final map includes cadastral boundaries, drain 
age lines, positions of trial holes and any other planimetric details that will 
assist the engineer to locate himself, including contours if the terrain is uneven. 
Areas of potential slope instability, seepage zones etc., are also shown on the 
map. 
Solid bedrock, whether in outcrop or at depth below the surface, is depicted 
in colour on the map, and the overlying soil strata are indicated by means of 
various standardised hatchings. In addition, the soil profile formula is given in 
symbols in each delineated area: e.g. in fig. 6 the formula p/SiSd/M refers to 
a soil profile consisting of scattered pebbles on surface, overlying a stratum of 
silty sand, overlying weathered mudstone and finally mudstone bedrock. 
Each map is accompanied by a report giving details of each mapping unit 
and the indicators by which it was distinguished on the airphotos. Suggestions 
are also made in the report as to the materials which are considered to hold 
most promise as good road materials: laboratory testing of these materials is 
then left to the discretion of the highway engineer. The quantities of materials 
available can be judged from the detailed soil profiles recorded from each 
trial hole and included in an appendix to the report. 
Conclusion 
1. It appears that considerable economic benefits can be effected in efficiency 
of planning and cost of construction if maps of this type are put to their full 
use by highway engineers. Intelligent use of the maps holds possibilities for 
better group classification of soils for design-test purposes, and sampling can 
be based on less empirical procedures. Particularly in areas where construction