Something is Rank in the State of Data

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Determining the best way to visualize ranked lists.

UMD iSchool News

Original Story by Niklas Elmqvist
Sparks of Innovation: Stories from the HCIL

In 1786, William Playfair (1759–1823) invented the bar chart, which conveys values using the length of a rectangle. He did this to help members of the British parliament — many of them illiterate — understand complex data without the need for actual numbers. The bar chart has since become one of the most prolific and familiar types of statistical data graphics, and is a staple in many infographics. Bar charts are commonly used to visualize many items side by side, such as the gross domestic product of countries, the unemployment rate in U.S. states, or the enrollment in different academic units at a university. Such lists are often sorted, and we thus refer to them as “ranked lists” and their visualization as “ranked-list visualization.”

However, while bar charts remain the dominant form of ranked-list visualization, they have an important drawback. As the picture above suggests, showing a long ranked list typically requires scrolling, as the whole list won’t easily fit on screen at the same time. For this reason, visualization experts have in recent years proposed several alternatives to bar charts.

For example, treemaps were originally designed for hierarchies, but are often used for ranked lists. In fact, their popularity is somewhat surprising since assessing the area of a rectangle is known to be more difficult than its length.

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