rately examining, describing, and symbolizing 
each component. 
(4) Allow, a¢ a@ maximum, inclusions that 
comprise as much as 20 percent of a delinea- 
tion; however, it is preferable to hold this 
limit to less than 10 percent of the delineation 
area. 
(5) Differentiate fact and existing condi- 
tions from interpretations of the examiner in 
gathering field data and in preparing initial 
maps. 
PHOTO INTERPRETATION OF RANGE 
RESOURCE FEATURES 
In doing really serious and effective aerial 
photo interpretation of rangeland features, 
people will tend to do a better job if they (1) 
have keen powers of observation and good 
stereo perception; (2) have had wide field ex- 
perience, making astute observations of ecolog- 
ical phenomena; (3) have a logical mind, ena- 
bling them to reason clearly and to fit together 
bits of evidence to form plausible conclusions; 
and (4) have a vivid imagination tempered by 
sound judgment. However, range resource peo- 
ple who lack some of these capabilities will be 
able to glean valuable information from 
good-quality aerial photographs. Some will do 
better than others, and a few individuals may 
only be able to use the photos as field maps. 
Even if you have been “interpreting” aerial 
photos for years, it is likely that you will be 
pleasantly surprised by the increased amount 
of information you can acquire from interpre- 
tation. It only requires that you carefully study 
the characteristics of aerial photo images and 
relate the unique images to the phytosociology 
and resource conditions of the area in which 
you work. 
Useful Image Characteristics 
The most successful and accurate aerial 
photo interpretation depends upon the care 
with which these subject-image relationships 
are worked out. Image characteristics that are 
most useful in the interpretation of range re- 
source features from conventional black-and- 
white aerial photography follow: TEXTURE 
of the images of individual plant communities 
or other features; SURFACE GEOMETRY of 
items discernible within each image, i.e., 
within the image of the plant community; 
PATTERN formed by adjacent images; 
SHAPES discernible within images, both two- 
and three-dimensional; SHADOWS of discern- 
ible objects; and finally, TONE SHIFT from 
image to image. 
Image tone shift is listed last because it is 
the most difficult to evaluate in the interpreta- 
tion of range resource features. Certain techni- 
184 
cal and operational problems in photography 
and photo reproduction make it necessary to 
consider primarily the tone shift, or relative 
difference in tone, from subject to subject 
rather than absolute shades of gray. Tone is a 
very complex image characteristic. In some in- 
stances, tone alone is highly significant; in 
other cases, it can be extremely misleading un- 
less considered along with additional image 
characteristics.’ 
Additional Considerations 
All serious aerial photo interpretation of 
rangelands should be done under stereoscopic 
examination. Mapping should normally be done 
without magnification or under not more than 
X2 power. After the delineations are made, 
taxonomic units can be identified; and the read- 
ing of other details from the photography is 
generally best done under X2 to X4 magnifica- 
tion. Except in special cases, higher power usu- 
ally reduces the field of view so that interpret- 
ability tends to be lost despite image magnifi- 
cation. 
Where one is working with photography 
from widespread areas, an important aid to 
correct interpretation is first to determine the 
geographic location of the stereo model. With 
this information, the interpreter is able to 
identify images from among logical possibili- 
ties and to exclude alternatives inconsistent 
with the location. 
Finally, one of the most important require- 
ments to enhance interpretability of aerial 
photography is to insist on higher standards of 
performance on image quality control. This ap- 
plies both to taking photographs and to re- 
producing prints. Besides the usual contract 
specifications, more attention needs to be paid 
to the proper season for photography. In this 
area, research is especially needed. For grass- 
land, shrub steppe, savanna, and desert areas, 
high-contrast film types should normally be 
specified. If range people really want to become 
serious about remote sensing as a day-to-day 
working tool, aerial photography specifications 
should require the use of high-resolution lenses 
properly filtered to achieve near state-of-the- 
art performance. Aerial contractors also need 
help in identifying the more critical vegetation 
types on which exposures should be based. 
Negatives should be very carefully screened 
for quality in terms of image densities and con- 
trast, and experienced vegetation interpreters 
should be regularly consulted in the review 
and acceptance of aerial photography. Even if 
good negatives are available, specifications on 
print quality are also in order. These should 
call for a higher degree of uniformity from 
2For definitions and additional details, consult the 
Manual of Photographic Interpretation. 
