INTERACTIVE OVERLAYS OF JOURNALS AND THE MEASUREMENT OF INTERDISCIPLINARITY

Document sets downloaded from the Web of Science can be projected onto global journal maps based on all journals contained in the Journal Citation Reports (JCR) of the Science and Social Science Citation Indices (2011). The disciplinary diversity of a downloaded set is then measured in terms of this map using Rao-Stirling's "quadratic entropy." Since this indicator of interdisciplinarity is normalized between zero and one, the interdisciplinarity of document sets can be compared among one another and across years, both cited and citing. The colors used for the overlays are based on Blondel et al.' s (2008) communityfinding algorithms operating on the 10,000+ journals included in JCRs. The results can be exported from VOSViewer with different options such as proportional labels, heat maps, or cluster density maps. The maps can also be web-started and/or animated (e.g., using PowerPoint). The "citing" dimension of the aggregated journal-journal citation matrix was found to provide a more comprehensive description than the matrix based on the cited archive.