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