A visual notation is a graphical representation. It consists of graphical symbols, their definitions, and a visual grammar. Some examples of graphical symbols are: lines, surfaces, volumes, textual labels and spatial relationships. These elements are used to build the visual vocabulary of a notation; Mind Maps for example, consist of lines and labels. Visual representations are effective because they convey information more concisely and precisely than language. They are also better remembered.

Source: New approach to designing visual notations