10 REPORT OF COMMISSION VII 
on Photo-Interpretation Research, Keys, and Techniques recently has devised 
and tentatively adopted the provisional definitions given in Figure 4 after pro- 
longed discussion and deliberation. The committee realizes that interpreters, 
of necessity, are on the threshold of introducing a great many new terms into 
the literature relative to keys. In the hope that a meaningful standard terminol- 
ogy may be employed in this field, the Committee is using several media, in- 
cluding this Report, for bringing these provisional definitions to the attention 
of those who will be concerned with photo-interpretation keys. It is requested 
that, prior to October 1, 1952, any comments relative to these terms be addressed 
to the author, c/o U.S. Naval Photographic Interpretation Center, Washington, 
25, D. C. These comments will be conveyed to other members of the Committee 
for consideration at the time when the Committee drafts its final recommenda- 
tions. : 
The purpose of a photo-interpretation key is largely two-fold; (1) to serve 
as an aid in training the photo-interpreter to recognize certain objects and con- 
ditions, and (2) to serve as a reference which the photo-interpreter may consult 
periodically to refresh his memory as to the distinguishing characteristics and 
general appearance of the various objects and conditions. 
The importance of a photo-interpretation key in each of the above respects 
becomes quite obvious when we consider that frequently, in a training period 
of a few weeks, the photo-interpretation student may be expected to learn to 
recognize virtually all natural and man-made features of the Earth's surface, 
and having recognized them to fit them into a pattern from which he can deduce 
the nature and significance of man's activity in the area, past, present, and 
future. It would be difficult to envisage a more comprehensive objective to be 
achieved in so short a training period. If this objective is to be realized, or even 
approximated, information given the student must be systematized and pre- 
sented in as concise a manner as possible. The rapidly growing enthusiasm for 
photo-interpretation keys is a logical consequence of this requirement. 
À determination as to which type of organization and presentation should be 
used in keying out any given group of objects or conditions usually is dependent 
upon two factors: (1) the number of object- or condition-classes to be recognized ; 
and (2) the variability normally encountered within each object- or condition- 
class. 
As an example of a relatively simple group, we might consider ''Dirigibles 
of the World" in which there are few classes to be recognized, the necessary 
recognition features of each class are few, and the variability within each class 
is slight, because all ''sister ships" are constructed from essentially the same 
set of blueprints. Such a group lends itself ideally to analysis with a disc or 
punch card type of key. 
As a relatively complex group, we might consider ‘Landforms of the World” 
in which there are many classes worthy of recognition, the necessary recognition 
features of each class may be many (Powers, 1951), and the variability within 
each class is large, because of secondary modifications effected by various 
erosional and depositional forces. Furthermore, certain of the salient photo 
recognition features of landforms may be partially or wholly obscured by 
vegetation. Because of the complexity of this group, it may not be possible 
to prepare an elimination key that will encompass all classes worthy of recogni- 
tion within the group. This fact may impose the requirement for preparation 
of several, if not all, of the various types of selective keys. 
By way of providing some specific examples of key-types, a group will be 
considered which is somewhat intermediate in complexity between the two