WORKING GROUP 3 
CURTIS 
157 
soils into drainage classes, i.e. excessive, free, imperfect, poor and very poor. 
The classes are determined by profile characteristics, especially the degree of 
mottling and gleying [Soil Survey Staff, 1960]. Although these characteristics 
are useful diagnostic features it is not certain that groupings derived from them 
form natural units. Therefore the surface conditions may not be wholly in 
accord with these groups. This situation was encountered in an assessment of 
the accuracy of photo interpretation of drainage classes made by the writer. 
An area of morainic drift country lying between Walton and Healaugh in 
Yorkshire was studied. A map showing areas of a. freely drained; b. imper 
fectly drained; c. poorly and very poorly drained soils was first produced by 
interpretation. The area was subsequently mapped on foot and the accuracy 
of interpretation was measured with a planimeter. The results were as follows: 
Areas of each drainage class interpreted as: 
determined by field 
observations 
mapped 
in field 
Freely drained 
Imperfectly drained 
Poorly to very 
poorly drained 
acres 
acres 
% of total 
acres 
% of total 
acres 
% of total 
Freely drained 
813 
497 
61.1 
286 
35.2 
30 
3.7 
Imperfectly drained 
Poorly and very 
1015 
— 
— 
785 *) 
77.3 
— 
~ 
poorly drained 
276 
4 
1.5 
62 
18.8 
220 
79.7 
*) The remaining 230 acres were interpreted as freely or poorly and very poorly drained 
which were present in about equal proportions. 
In this example the surface characteristics showed a better correlation with 
the boundaries of poorly and very poorly drained soil profiles than with freely 
and imperfectly drained profiles. For interpretation purposes it would be 
better to abandon profile drainage characteristics and adopt instead surface 
drainage characteristics. For example soils can be grouped on photographs 
according to the surface drainage of the site, e.g. Shedding Sites, Normal Sites, 
Receiving Sites, etc. [Soil Survey Staff, 1960]. If photo interpretation is to 
play its full part in aiding soil surveys a new approach to the definition of soil 
mapping units must be sought. 
References 
American Society of Photogrammetry (1960). Manual of Photographic Interpretation. 
Soil Survey Staff (1951). Soil Survey Manual. 
Soil Survey Staff (1960). Soil Classification: a comprehensive system, 7th Approximation. 
Pomerening, J. A. and M. G. Cline (1953). The accuracy of soil maps produced by various 
methods that use aferial photo interpretation. Photogrammetric Engineering, 19. 
Avery, B. W. (1956). A classification of British Soils. Transactions VI International Congress 
of Soil Science. 
Buringh, P. (1954). The analysis and interpretation of aerial photographs in soil survey and 
land classification. Netherlands Journal of Agricultural Science. Voi. 2. No. I. 
Veenenbos, J. S. (1956). Small-scale pedological analysis and map compilation. Transactions 
VI International Congress of Soil Science.