Data Vis: Position in a Scale
Research performed by William S. Cleveland and Robert McGill, as seen in their paper Graphical Perception: Theory, Experimentation, and Application to the Development of Graphical Methods, shows one of the best visual qualities to use for powerfully meaningful charting is the position.
The most obvious example for using this principle in a chart is the scatterplot. On the scatterplot, symbols represent counts of specific things and their relationship to each other is shown along a scale. The scale can either be time or some other open value that fits along the axis.
Another way to use this principle is in combination with other principles with something a little more creative. A good example of that is to use floating bars that have a specific meaning based on their position. The length of the bar would have a different meaning.
