requirments such as symbolization for future charting when air speeds will 
have been greatly increased. What can we do to these charts to make it 
easier for the navigator to recognize what he sees portrayed there; how should 
jet charts be designed to make instant selection and recognition of features 
infallible? Answers are being correlated and ideas with possibilities are 
being tested almost daily. Several years ago the shaded relief process was 
conceived and applied to maps for use on the ground. Quickly it was applied 
to the standard aeronautical chart also, but is was not widely accepted. 
Today, however, the process is being revived for use on many of our charts 
and with apparent success. At the same time different color combinations 
are being introduced for field testing. Too, a type of gradient tinting is 
being considered. The latest development is to base the tint layers on varia- 
tions of slope rather than strictly contour lines or segments of elevations. 
In conjunction with shaded relief and a pictorial means of accentuating the 
high points, a definite improvement is noticeable. The combined art is not 
confined to one type of chart; the technique may be carried over into as 
many series as is possible regardless of scale. Requirements demand an 
accurate portrayal of the earth’s surface features and our cartographers 
must satisfy the demand. All of this work requires understanding of the 
earth’s features, for which photo-interpretation experience is invaluable. 
5. Chart requirements have been discussed with regard to scale and 
symbolization, and their direct effect on the cartographers photo-interpreta- 
tion ability has been pointed out. Now let us look into the photography 
requirement in similar respect. Generally, Air Force photography should 
provide the maximum coverage possible per exposure and yet retain the 
detail necessary to meet charting requirements. This implies that a certain 
amount of detail will be sacrificed. Dependency is placed on the carto- 
grapher with his photo-interpretation skill to supply the missing detail where 
necessary. You can understand then, why he is so concerned with the 
attainment of maximum resolution in the photographs supplied him; the 
higher the resolution, the better the odds are that his duty will be more 
easily and accurately accomplished. We feel that minimum average weighted 
resolution should be at least twenty lines per millimeter (20 lines/mm) for 
vertical charting photography. This is based on cameras and the ceilings of 
photographic aircraft now in service as principal controlling factors. The 
improvement of the altitude-resolution ratio is definitely a main concern of 
Air Force charting which will affect our cartographer in his photo-interpre- 
tation capacity. Study of controlling factors is continuous at ACIC. 
6. Many conditions limit progress today in extending our altitude-resolu- 
tion ratio. Photographic missions accomplished at the 40,000 foot altitude- 
level provide 1:80,000 scale six-inch wide-angle photography. During World 
War II a new method of using charting photography was inaugurated. It is 
frequently referred to as “Trimetrogon” since it employs three metrogon 
cameras which produce three simultaneous and overlapping exposures. Each 
set of three consists of one vertical exposure and two high obliques which 
are directed normal to the flight line and in opposite directions. Complete 
coverage then, means that overlap of flight lines is actually overlap of opposite 
obliques. The identification of images on these obliques requires a special 
photo-interpretation ability on the part of the cartographer. Perhaps the 
most difficult task is the transfer of identifications between adjacent flight 
strips from oblique to opposing oblique when exposure stations may be 
separated by 20 to 30 miles, and when nadir points are over 200 miles from 
apparent horizons. The basic technique employed is that of mass area 
identification from which individual features or small groups of features can 
be selected for control or other charting purposes. Areas of mass identifi- 
cation vary in size, with the average area covering many overlapping photo- 
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