What does "data-ink ratio" refer to in the design of charts and graphs?

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Accepted Answer

The proportion of a graphic's ink that is used to present actual data versus non-data elements like decorative borders and unnecessary gridlines, with a higher ratio being preferred. The data-ink ratio, a concept introduced by Edward Tufte in his seminal work "The Visual Display of Quantitative Information," refers to the proportion of a graphic's total ink (or pixels, in digital display) that is devoted to presenting actual data versus non-data elements such as decorative borders, unnecessary gridlines, redundant labels, and chartjunk. Tufte advocates maximizing the data-ink ratio by removing non-essential elements that do not communicate data, resulting in cleaner, more effective visualizations. This principle encourages technical writers to create charts and graphs that communicate data clearly without visual distractions.

The literal calculation of ink used to print a chart divided by total page ink takes the concept too literally - the data-ink ratio is a design principle about the proportion of visual elements dedicated to data representation, not a literal measurement of ink volume. The ratio of text to images in a document describes the overall document's text-to-visual balance, which is a different layout consideration from the internal design quality of individual charts. The contrast ratio between text and backgrounds describes an accessibility metric for readability, not the data presentation efficiency concept that the data-ink ratio addresses.

The data-ink ratio and related visual design principles are advanced but testable concepts on the Technical Writing DSST exam. Students should understand Tufte's principle of maximizing data-ink ratio, the concept of "chartjunk" (unnecessary visual elements that distract from data), and practical applications of these principles when creating or evaluating charts, graphs, and other data visualizations in technical documents.

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