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Transactions of the Symposium on Photo Interpretation

tion of 1 : 16,000 vertical photographs, and the data is directly plotted onto
1 : 50,000 topographic maps. The classification is grouped to allow ready
reduction to 1 : 250,000, though this will mean the loss of detail divisions.
Further reduction to 1 : 500,000 or 1 : 1,000,000 can be envisaged, to be
comparable with the existing reconnaissance survey.
Field checking in this type of survey has varied from 90% of all types isolated
to less than 5%, primarily depending on the access possible in the area con
cerned. The most satisfactory approach has been selective checking of approx
imately a 10% sample.
This method is of greatest value in pre-fieldwork familiarization in regional
or systematic studies. The steresocopic photo examination has allowed surface
routes and campsites to be picked in remote areas, and the maps produced
form a definite start to concentrated fieldwork [54]. It has also been used with
excellent results when the 1 mile base maps were replaced with planimetric
tracings from a mosaic of 1 mile : 1 inch vertical photography [56].
Most geographical studies of a local or sub-regional nature, particularly
those applying to the major part of regional planning, fall into the category of
large scale survey.
The techniques that have actually been used have depended a great deal on
the survey requirements and on the training of the photo user. This last factor
has been strongly influenced by the complete availability of Canadian air
photographs to all segments of the community, including local municipal
authorities, local government agencies, and others with a particular planning
project but not necessarily a geographic or photo interpretation background.
The most straightforward application has been the plotting of relatively
static forms, such as the physiography of almost any area [16, 24] and the
vegetation patterns in the more remote areas [22, 26]. This type of interpre
tation has been mainly carried out from 1 : 16,000 (1,320 foot : 1 inch) photo
graphs, and has resulted in maps of micro-drainage [57] soil type and soil depth
for town planning and regional planning [45, 58, 59], assessment of existing
forests, land use and access for selection of recreational areas [40, 42, 43, 44],
isolation of physiographic units as a base for zoning planning [52], and out
lining of shore erosion areas [53].
The data is frequently outlined on the actual air photographs at contact
scale while under stereoscopic examination, and either used in that manner, or
transferred optically or by eye to available base maps or mosaics at approx
imately the same scale or to transparent overlays to fit over suitable mosaics or
Interpretation of the surface elements subject to relatively rapid change
is a more difficult problem. Such interpretation includes that applied to land
use in heavily populated areas, urban analysis, investigation of rapid geo-
morphic processes and transportation studies.
Occasionally, the existing maps are more dated than available photography