derived from aerial photos are certainly not obtainable from 
ERTS, but such deficiencies are balanced by the synoptic over 
views that provide information which can be obtained from no 
other source. The interpreter can utilize this information 
effectively as long as the imagery is considered as an additional 
new tool with certain known limitations. 
ERTS images are especially valuable for studying very large 
parts of the world where this data represents the first detailed 
coverage of surface features, since only very broad reconnaissance 
surveys are available for these areas. This applies particularly 
to inaccessible, high mountains, large deserts, tundra and 
steppes, and polar regions. Most of all, ERTS images provide 
up to date basic information to developing countries or under 
populated, large countries for the study of their natural 
resources. 
There is a growing literature about the useful applications 
of ERTS-1 images in various disciplines. It is contained mostly 
in proceedings of remote sensing conferences. The proceedings 
of the NASA Symposium on Significant Results Obtained from 
ERTS-1 and the Third ERTS Symposium (NASA, 1973), in particular, 
contain most valuable and interesting results. 
The appended selection of ERTS images from three continents 
serve to illustrate some of the many observable features that are 
relevant to skilled visual interpretation. In these illustra 
tions, line drawings and similar cartographic work has been 
avoided in order to show that ERTS images do not require that 
kind of modification. No cartographic work could yield as much 
fine detail of the features represented on the image in their 
original scale. Unless it is absolutely necessary for 
presentation purposes, line drawing should be avoided. 
Figure 1 illustrates a portion of the Canadian Shield in 
Ontario. The image represents a winter scene with the snow 
enhancement of the surface topography. The relief of the earth’s 
surface reflects the physical characteristic of the underlying 
rocks and geological processes. Many geomorphic features can 
be identified mainly by the recognition of form and pattern 
which relate to the structural characteristics of a certain 
rock type. The Canadian Shield contains a number of alternating 
volcanic and sedimentary rich, oragenic belts together with 
irregular granitic masses. These rock types can be recognized 
and identified on ERTS imagery by their different lithological 
and structural patterns. This interpretation can be useful in 
mineral exploration (Palabekiroglu, 1974). 
Massive homogeneous, granitic-type rocks constitute the 
main part of the Canadian Shield. Their lithological and 
structural characters are reflected on the ERTS imagery by a