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SYMPOSIUM PHOTO INTERPRETATION, DELFT 1962 
airphoto coverage of the search area and all relevant maps - such as recent 
agricultural soil-survey maps and surficial geologic maps. In cultivated areas 
of the prairies, 4 inch = 1 mile photos (1 : 15,840) are usually available. In 
non-agricultural northern areas and in mountainous regions, photos to scales 
of 1 inch = 2640 to 3333 ft (about 1 : 30,000 to 1 : 40,000) are most frequently 
used. 
All delineations are made right on the photos as a result of careful stereos 
copic study. Annotations are made which disclose the interpreter’s predictions 
about quality, quantity, mode of deposition of a deposit, expected variability, 
best places to explore in the field, and chances of deposit meeting required 
specifications. The outline of granular prospects and pertinent notes about 
each deposit are then transferred to a small-scale plan of the search-area. 
(fig. 1). Marked photos may be referenced to a mosaic, to a photo-index sheet, 
Fig. 1. Self-explanatory map prepared 
from airphotos. Shows occurrence of 
several common glaciofluvial deposits 
within a relatively small area. Each 
square represents one square mile. 
to a map showing the legal survey system, or to planimetric maps. A covering 
report accompanies the maps and photos sent out to the client. Upon receipt 
of this information, the client’s field engineers will know where to check each 
prospect in the field; they should know how to get to a prospect on the ground 
and know what to look for when they get there. 
Where Photo Interpreter Checks His Own Interpretive Work 
The sequence here is very similar to the one described above. The aerial 
observer usually assembles annotated contact prints into a rough laydown 
mosaic, (fig. 2). In this way all prospects in the search-area can be seen at a 
glance. The order of checking prospects and all roads and trails to be followed 
in the field are appropriately indicated on the mosaic in color. This simplifies 
field work. Field notes are referenced to the different prospects indicated on 
the mosaic. 
Photos are studied stereoscopically a second time in the office in the light 
of field evidence. A final map is then prepared, giving as much pre-subsurface