Data-Ink Ratio

Definitions

Tufte defines two types of ink used to construct a graph:

• data-ink - the essential non-erasable ink used to present the data
• non-data-ink - the redundant ink used to elaborate or decorate the graph

The Data-Ink Ratio is defined as the percentage: (100 x Data-ink) / (Total ink used on graphic)

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Introduction

The Data-Ink Ratio is a concept published by Tufte in [Tufte83]. It arose from Tuftes goal "Above all else show the data".

"A large share of ink on a graphic should present data-information, the ink changing as the data change. Data-ink is the non-erasable core of a graphic, the non-redundant ink arranged in response to variation in the numbers represented."

The data-ink ratio is the proportion of ink (or pixels, when displaying information on a screen) that's used to present actual data, without redundancy, compared to the total amount of ink (or pixels) used in the entire display, such as in a table or graph. The goal is to design a display that has the highest possible data-ink ratio (that is, as close to the total of 1.0 or 100% as possible), without eliminating something that is necessary for effective communication.

Example

First an example of a graph with a low Data-Ink Ratio

How much of the ink on this chart could be removed without loss of information?

• The word "Year" is superflous
• Only the first year needs to include the digits 19
• Either the data labels or the vertical scale could be removed
• The y-axis label is duplicated in the title
• The bars need not be coloured

Now an example of a graph with a high Data-Ink Ratio