Ciro Cattuto wrote a simple piece of code that builds and visualizes a network of inferred semantic relations among the tags that Flickr users attach to their photos.
This is a proof of concept for an animation of tag-volume over time. The horizontal rule represents the passage of time, and the vertical rule represents the overall volume of tags at any given point.
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M. Hearst, and D. Rosner. HICSS '08: Proceedings of the Proceedings of the 41st Annual Hawaii International Conference on System Sciences, page 160. Washington, DC, USA, IEEE Computer Society, (2008)