Eigenfactor.org is a non-commercial academic research project sponsored by the Bergstrom lab in the Department of Biology at the University of Washington. Eigenfactor ranks journals much as Google ranks websites. Scholarly references join journals together in a vast network of citations. Eigenfactor uses the structure of the entire network (instead of purely local citation information) to evaluate the importance of each journal.
In a cooperation between Eigenfactor and the immensely talented Moritz Stefaner, a set of 4 interactive visualizations based on the Eigenfactor Metrics and hierarchical clustering were produced in order to explore emerging patterns in citation networks. A subset of the citation data from Thomson Reuters' Journal Citation Reports 1997-2005 was used in this endeavour, which encompassed, at the journal level, approximately 60,000,000 citations from more than 7000 journals over the past decade.
The first image represents a radial visualization based on hierarchical edge bundling, which gives an overview of the whole citation network. The colors represent the four main groups of journals that are further subdivided into fields in the outer ring. The segments of the inner ring represent the individual journals, scaled by Eigenfactor Score. In the initial view, the top 1000 citation links are plotted. Line size and opacity represents connection strength. The Bezier curves follow the hierarchical cluster structure, using the hierarchical edge bundling technique (pdf). Selecting a single journal (inner ring) or whole field (outer ring) displays all citation flow coming in or out of the selection. The color is based on the cluster color of the origin node. "I love the organic feel the bundled splines bring in, and multiplying the line colors added that deep extra color twist" explains Moritz on the most aesthetically striking visualization of the set.
The second image is a network visualization that puts journals, which frequently cite each other, closer together. You can drag the white magnification lens around to enlarge a part of the map for closer inspection. Clicking one of the nodes will highlight all its connections. If a journal is selected, the node sizes represent the relative amount of citation flow (incoming and outgoing) with respect to the selection; otherwise, they are scaled by their Eigenfactor Score.
You can read more about the project on Moritz's blog.