The principle of proportional ink

The principle of proportional ink, coined by Bergstromm and West in 2016, states that the sizes of shaded areas in a visualization need to be proportional to the data values they represent.

• Ink commonly refers to any part of the visualization that deviates from the background color: lines, points, shared areas, text.

• This principle refers to bar graphs or area graphs where the height and the length of the bar represent the data shown. This does not apply to dots or points on a graph, for example.