Then, in 2002, a young photo-sharing site called Flickr needed a way to show how users had classified, or “tagged,” their images. Borrowing Flanagan’s idea, Flickr added a “tag cloud” that showed the popularity of various tags using font size. The resulting graphic (Figure 3), which had a distinctive jumbled quality and whose most prominent words included “wedding,” “beach,” and “Nikon,” provided an instant overview of the site’s pictures and gave this kind of graphic a name.

Other tag-based sites, such as
del.icio.us and Technorati, fol-
lowed Flickr’s lead and the tech-
nique soon became a hallmark
of Web 2.0 design. These tag
clouds function as aggregators
of activity being carried out by
thousands of users, summariz-
ing the action that happens
beneath the surface of socially
oriented websites. Two years
after Flickr’s tag cloud appeared,
John Maeda—renowned graphic
designer and computer scientist
at the MIT Media Lab—declared
this type of graphic “The
Greatest Diagram of 2004” [ 4].
Today it seems like any site with
tags exhibits its own flavor of
visualization.

Aggregation of tags, however, is not the only use of tag clouds. There have been several attempts at using this technique for analytical tasks as well. These usually boil down to the examination of textual documents ranging from political speeches (Figure 4) and collections of blog posts to academic articles and entire books. Some of these efforts incorporate time, allowing users to quickly examine a collection of sequen-

 Figure1: Stanley Milgram”s collective mental map of Paris. Figure1: Stanley Milgram”s collective mental map of Paris.

 Figure 2: Figure 2: Fortune magazine: “Money Makes the World Go ”Round.” magazine: “Money Makes the World Go ”Round.”

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