what is Tag cloud ?

Definition

A word cloud of the content of this article.
A tag cloud is a set of related tags with corresponding weights. Typical tag clouds have between 30 and 150 tags. The weights are represented using font sizes or other visual clues. Meanwhile, histograms or pie charts are most commonly used to represent approximately a dozen different weights. Hence, tag clouds can represent many more weights, though less accurately so. Also, frequently, tag clouds are interactive: tags are hyperlinks typically allowing the user to drill down on the data.

History

The first use of tag clouds on a high-profile website was on the photo sharing site Flickr created by Flickr co-founder and interaction designer Stewart Butterfield. That implementation was based on Jim Flanagan's Search Referral Zeitgeist, a visualization of Web site referrers. Tag clouds have also been popularized by Del.icio.us and Technorati, among others.

The first published appearance of a tag cloud (or at least a weighted list) can be attributed to the "subconscious files" in Douglas Coupland's Microserfs (1995).

Prior to weighted list representation of tag clouds, paper maps had used the concept of weighted font size and font weights to represent relative size or importance of towns and cities.

Visual appearance

A data cloud showing stock price movement. Color indicates positive or negative change, font size indicates percentage change.

Tag clouds are typically represented using inline HTML elements. APML (Attention Profiling Markup Language) is often used to store and import/export Tag Clouds. The tags can appear in alphabetical order, in a random order, they can be sorted by weight, and so on. Some prefer to cluster the tags semantically so that similar tags will appear near each other. Heuristics can be used to reduce the size of the tag cloud whether or not the purpose is to cluster the tags.