United States Department of Transportation
i
Comparative readability of enroute low altitude charts with and without terrain depiction.
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1978-04-01
[PDF-399.61 KB]
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Abstract:The U.S. National Ocean Survey has issued an experimental copy of Enroute Low Altitude Chart L-3/4 dated April 21, 1977, as part of a program to explore the feasibility of introducing terrain depiction on the charts. The FAA's Air Traffic Service (AAT-1) requested the Office of Aviation Medicine to determine what derogatory effects such a change might have on the usability of the charts.
It was found in the study that shaded terrain depiction reduces readability of alphanumeric data as measured by increases in reading errors and reading time. Losses are attributed to the low figure-to-ground contrast ratios between the chart legends and the terrain background. Losses are most pronounced for alphanumeric data printed in small character sizes and with light inking densities. Losses are also evident for some large character sizes and heavy inking densities where mountainous terrain is depicted by heavy inking densities. Losses are particularly evident under low luminance levels but also occur to a lesser extent at elevated luminance levels.
Differences between the experimental and standard versions of the charts are least pronounced when the terrain depiction introduced only a moderate reduction in figure-to-ground contrast level and the items were viewed at elevated luminance levels.
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