Journal maps, interactive overlays, and the measurement of interdisciplinarity on the basis of Scopus data (1996–2012)

Using S copus data, we construct a global map of science based on aggregated journal–journal citations from 1996–2012 ( N of journals = 20,554). This base map enables users to overlay downloads from S copus interactively. Using a single year (e.g., 2012), results can be compared with mappings based on the Journal Citation Reports at the Web of Science ( N = 10,936). The S copus maps are more detailed at both the local and global levels because of their greater coverage, including, for example, the arts and humanities. The base maps can be interactively overlaid with journal distributions in sets downloaded from S copus, for example, for the purpose of portfolio analysis. R ao‐ S tirling diversity can be used as a measure of interdisciplinarity in the sets under study. Maps at the global and the local level, however, can be very different because of the different levels of aggregation involved. Two journals, for example, can both belong to the humanities in the global map, but participate in different specialty structures locally. The base map and interactive tools are available online (with instructions) at http://www.leydesdorff.net/scopus_ovl .