Interdisciplinary research (“IDR”) is often trumpeted as essential for scientific and technological advancement. However, interdisciplinarity is an ambiguous and multidimensional concept: there are several legitimate perspectives on how to track it --and a lack of consensus on which are the most appropriate.

This website offers a novel tool, the overlay maps of science, as a method to explore the degree of interdisciplinarity of a set of publications. The overlay technique visualizes the spread of publications over the global map of science, i.e. the structure of science as obtained from the analysis of cross-citations between disciplines.

The analysis can be carried out at different units of aggregation: for example for a university or corporation, for a research topic, or for a research programme or funding agency. By locating the publications over the map of science, one can gain an understanding of the diversity of disciplines involved. Since attribution of publications to disciplines is problematic and controversial, the overlay maps are only reliable with large numbers. We have estimated at least 70 publications may be needed for an exploratory map, but we recommend above 1,000 for accurate representations (see details in appendix in Rafols, Porter and Leydesdorff (to appear)).

The maps allow one to intuitively perceive various aspects of disciplinary diversity. First, the number of disciplines involved. Second, the balance of disciplines, i.e. –whether publications are evenly distributed or some disciplines are predominant. Third, and crucially, the cognitive distance between the disciplines involved –whether the research investigated covers disparate or cognate areas of science. This aspect of disparity is a key advantage of the maps: they differentiate between short-range interdisciplinarity (e.g. chemistry and physics), or long-range interdisciplinarity (e.g. social science and biology). Measures of interdisciplinarity can be associated with these maps, as described in Porter et al. (2007) and Rafols and Meyer (2010).

The overlay maps provide just one perspective on interdisciplinarity –namely the disciplinary diversity of publications. We suggest that other aspects be considered as well when assessing interdisciplinary research. Within the bibliometric remit, we believe it is equally important to explore degree of knowledge integration, i.e. whether the publication set under study constitutes or not a coherent (i.e. directly interrelated) body of research (Rafols and Meyer, 2010). More generally, we warn the users about the limitations of bibliometric tools to capture the complex processes involved in interdisciplinary interactions.

Please do not hesitate to contact us for questions and feedback!

Alan Porter and Ismael Rafols
School of Public Policy, Georgia Institute of Technology
SPRU (Science and Technology Policy Research), University of Sussex


This website was developed with support from the Science of Science Policy Program, SBE Award #0830207. The findings and observations contained here are those of the authors and do not necessarily reflect the views of the National Science Foundation.