Angular Readability
The visual presentation of any object is bordered by angles. The presentation of the angles can be less readable, depending
on:
 angles that approach the 0° or 180°  axis.
In general, there is a need to differentiate between two types of angles:
 Clearly legible angles:
Clearly legible angles are perceived by taking a deep look at each element on the elementary level on a map.
 The "vague" angle:
This angle can just be seen, within the entire image. For example: In a 2D diagram this one points out the relationship between
the 2 aspects of the x and y axis.
For further explanation have a closer look at the following graphic, a diagram that could be part of a legend on a thematic
map:
Legible and Vague Angles 
In graph A, , the net and legible angles are perceived at once because they are close to 70°, an optimal stage for angle readability.
The secondary vague angle (blue line) is too weak and almost invisible. In contrast to A the vague angle perfectly visible in B (blue line), but here the disadvantages of the clearly legible angles appear. They are close to 0°. Finally, the angular
legibility is ideal in graph C: It corresponds to a compromise between the elementary and secondary level of reading. Neither acute angles or obtuse angles
are used and neither a long or too higher stretched diagramform chosen.

Test your knowledge of angle readability with the following animation.