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SYMPOSIUM PHOTO INTERPRETATION, DELFT 1962 
terrain. Patterns were much more distinctive in recent alluvial and floodplain 
terrace areas than elsewhere. 
In general, however, the cartographic scale is too large: the discontinuity 
of the various features of the landscape - its diverse geology and land use - 
makes its basic character apparent only at a smaller scale. 
Discussion 
Ing. Pascaud (France): What was the scale of the photographs used and what was the density 
of observations in the conventional soil survey? Answer: The scale was 1 : 12,000; the density 
of field observations varied between 1 boring per 2 to 4 acres. 
Mr. Tomlinson (Canada) asked what was the ratio between time spent on photo interpretation 
and time spent in the field. Answer: Photo interpretation took only about 14 hours of office 
work. 
Mr. P. Jongen (France) remarked that in Africa south of the Sahara photo interpretation on 
scales 1 : 10,000 to 1 :20,000 is made before the field work is carried out, so that a more rational 
choice of field observations may be made. After the field work has been carried out, the photo 
interpretation makes it possible to draw the soil boundaries with a greater precision. In this 
system the density of field observations is 3 observations per 10 ha for maps on scale 1:10,000 
and 1 to 2 observations per 10 ha for maps on scale 1:20,000. 
Mr. L. F. Curtis (U.K.) commented that before detailed mapping begins it is usually necessary 
to carry out a reconnaissance survey. In a reconnaissance survey of North Kelsey and South 
Kelsey, Lincolnshire, it was found that photo interpretation greatly aided the work. Thus 
photo interpretation may be useful in the early stages of a detailed survey. Mr. Jarvis replied 
that he is now changing over to more reconnaissance mapping. 
Mr. R. Webster (U.K.) noted that Mr. Jarvis finds air photo interpretation more difficult 
in erosional than in depositional landscapes. The soil boundaries in erosional landscapes are 
frequently more diffuse, and not only because of solifluction. Bearing this in mind, does the 
speaker think that it is possible to predict, reasonably confidently, the nature and sense of 
change in soil conditions in terrain of this type, even though it is not possible to draw bound 
aries with certainty? Mr. Jarvis answered that, owing to the diverse nature of the superficial 
deposits, he has found it difficult to do so. 
Dr. R. M. S. Perrin (U.K.) wished to emphasize the danger of using land use for soil predic 
tions. The presence of a factory taking some particular crop, such as peas or sugar beets, often 
distorts the pattern over a large area. Would the author or Dr. Vink care to comment further? 
Mr. Jarvis remarked that land use is dependent on so many factors in England, that it is not a 
reliable guide to soil conditions. Dr. Vink (W.G. chairman) remarked that land use is certainly 
a guide to soil conditions, but that the actual land use boundaries always diverge from the 
soil boundaries. Therefore he uses land use as an “element of interpretation”, but wherever 
possible in combination with one or more elements of a morphological nature.