velopment of tridimensional vision. 
The scale of human perception is proportional to the acuteness and 
to the amplitude of our perceptive organs and to the purpose we 
are destining our observation. 
Nature consists mainly of discrete objects: trees, animals,rocks, 
human beings, etc. 
The human mind is adapted to organize the phenomena into segments 
and to set them in order according to its levels of experiments, 
which are transferred to the involving physical reality. 
The "MANUAL OF PHOTOGRAPHIC INTERPRETATION", 1975, of the AMERICAN 
SOCIETY OF PHOTOGRAMMETRY defines Photointerpretation as "the act 
of examining photographic images at the aimof identifyin objects 
and determining its meanings". It points out as well that aerial 
photographies are the raw material for photointerpretation. 
A great deal of information can be obtained from a sole aerial 
photo, due to the daily subsistence of man upon his habitat. The 
use of stereoscopes, which render the visualization of the con 
tents of images in the third dimension easier, offers a solid foun 
dation for photointerpretation. Besides, there are the elements 
of image interpretation, aiming at helping in interpretation, as 
objects may appear in photos in hundreds or thousands of varia 
tions: Size, Shape, Shadow, Tone and Color, Texture, Pattern, Si 
te, Association and Resolution. 
Photointerpretation is connected to some branch of human knowledge, 
therefore not existing by itself; so, according to the. American 
Society of Photogrammetry, it may be applied to t h e following 
Sciences: Agronomy, Archaeology, Astronomy, Biology, Ecology,Geo 
graphy, Geology, etc. It is up to the photointerpreter to develop 
abilities through the study and inference of the phenomena to be 
exploited in the aerial photographies. 
Besides, there is a set of factors which regularize the quality of 
the works of photointerpretation: the person performing the work, 
types of photographies and available instruments; objective of 
the interpretation, scale and other specifications of the m a p 
and ready for use correlate knowledge. 
The great majority of subjects in which photointerpretation pro 
cesses are applied, undergo the following periods of probation: 
a) detection; b) recognition and identification; c) analysis; d) 
conclusion; e) classification; f)- idealization. The: first pre 
sents a direct relationship with the visibility of the objects 
to be interpreted, depending on: type of object, type of subject, 
type of scale and quality of photographies. The second step esta 
blishes "what the object is". Sometimes this step is called Pho 
to-Reading. The analysis outlines groups of objects having an 
identifiable individuality by photointerpretation. The process 
of conclusion is the most complex one as it is based on the con 
vergency of evidence, leading to classification, thus establish 
ing the identity of the surfaces or objects. Through idealiza 
tion, the lines of what is really seen on the photoimage are wor 
ked out. 
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