The data-ink ratio is a term and design principle coined by Edward Tufte. Tufte refers to the amount of ink required to print points that represent relevant and meaningful data in a graphical display. Data ink in itself is the visual information, the core that represents the data, and that cannot be erased without loss of meaning.
Tufte defined the data-ink ratio as data-ink / total ink used by the graphic = 1 – proportion of a graphic that can be erased without loss of data.
In dashboard design the data-ink ratio refers to the pixel density of data represented versus non-essential pixels. The amount of redundant pixels should be kept to a minimum.
Five examples of non-data pixels in dashboard design and how they can be altered to achieve a better data-ink ratio.:
- Diagrams and bar graphs that use color codes that bear no meaning should be simplified. For example all bar graphs could use the same color.
- Using 3D effects to render real-world objects should be reduced to work in 2D and without gloss
- Using real-world objects to represent data (such as gauges, dials, cockpits, etc.) should use simple graphical visual representations instead
- Using boarders around individual displays that are related should be avoided so that relationship between data sets is clear
- Using strong competing colors in dashboard areas that contain secondary or tertiary information should be avoided and instead muted.