1.3.9-6 Clearly Discriminable Shapes

Shapes used in coding for data groups should be clearly discriminable.

Additional Information:
When shape coding is used, the shapes should vary widely and the number of basic shapes should be limited. For example, the elements of one group in a display might be triangles and the elements of a second group might be circles. Approximately 15 different shapes can be readily distinguished, provided the shapes are properly designed. Under adverse viewing conditions, no more than 6 shapes should be used. When needed, other highlighting and graphic techniques (color, filled vs. unfilled, and other 'modifiers') should be used to display different states or qualities of the basic symbol.