Image by Marc_Smith
This is a treemap of the Usenet newsgroup discussion community space generated by the Netscan system at Microsoft Research. This map presents the number of unique authors in each Usenet newsgroup who appeared in the current and prior year. Data on the number of "returnees" in each newsgroups was collected and calculated by the Netscan service. The area of each box is proportional to the number of authors that newsgroup attracted in both the current and prior year. Newsgroups with bigger returnee populations create bigger boxes. Color maps to change from the prior year, green indicating growth and red for decline over the prior time period. The original sized image shows significant detail. The treemap tool is available for free download from the research.microsoft.com web site. It comes with an Excel plug-in that allows users to generate their own treemaps with any data they can get into a spreadsheet (that contains a properly formatted hierarchical data structure). Your mileage may vary. Netscan can be found at netscan.research.microsoft.com.
Smith, Marc A., Researcher at Microsoft Corporation, 2007. Netscan: A Social Accounting Search Engine, Microsoft Research Community Technologies Group, netscan.research.microsoft.com