Global maps of science based on the new Web-of-Science categories
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- Leydesdorff, L., Carley, S. & Rafols, I. Scientometrics (2013) 94: 589. doi:10.1007/s11192-012-0784-8
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In August 2011, Thomson Reuters launched version 5 of the Science and Social Science Citation Index in the Web of Science (WoS). Among other things, the 222 ISI Subject Categories (SCs) for these two databases in version 4 of WoS were renamed and extended to 225 WoS Categories (WCs). A new set of 151 Subject Areas was added, but at a higher level of aggregation. Perhaps confusingly, these Subject Areas are now abbreviated “SC” in the download, whereas “WC” is used for WoS Categories. Since we previously used the ISI SCs as the baseline for a global map in Pajek (Pajek is freely available at http://vlado.fmf.uni-lj.si/pub/networks/pajek/) (Rafols et al., Journal of the American Society for Information Science and Technology 61:1871–1887, 2010) and brought this facility online (at http://www.leydesdorff.net/overlaytoolkit), we recalibrated this map for the new WC categories using the Journal Citation Reports 2010. In the new installation, the base maps can also be made using VOSviewer (VOSviewer is freely available at http://www.VOSviewer.com/) (Van Eck and Waltman, Scientometrics 84:523–538, 2010).
KeywordsMap Overlay Web of Science Subject categories Interdisciplinarity
Changes in the organization of subject categories and subject areas between versions 4 and 5 of WoS
WoS version 4
WoS version 5
Subject categories (SCI + SoSCI)
222 ISI subject categoriesa
225 WoS subject categories
Abbreviation in the download
25 ISI subject categories
26 WoS subject categories
151 subject areas; abbreviated SC in the download
Whereas previously 18 factors were found most appropriate for explaining the structure of the aggregated citation matrix, an organization into 19 factors explaining 54.3 % of the variance is most apt for showing the disciplinary structure of the new matrix. The changes are mainly in the organization of mathematics. Rafols et al. (2010, at p. 1876) already noted that “the position of mathematics (all math subject categories) in the map remains open to debate. Since different strands of mathematics are linked to different major fields (medicine, engineering, social sciences), these may show as diverse entities in distant positions, rather than as a unitary corpus, depending on metrics, classifications, and clustering algorithms used.”
Distinction between “computer science” and “mathematical methods” in terms of WoS subject categories
12 WC attributed to “computer science”
6 WCs attributed to “mathematical methods”
Computer science, hardware and architecture
Computer science, interdisciplinary applications
Engineering, electrical and electronic
Operations research and management science
Computer science, artificial intelligence
Computer science, theory and methods
Statistics and probability
Computer science, information systems
Automation and control systems
Computer science, cybernetics
Computer science, software engineering
Imaging science and photographic technology
Transportation science and technology
As with our previous installation, the base map with the relevant initialization routine for Pajek (v. 2.05) is available on the internet. The new base map can also be used as input to VOSviewer (Van Eck and Waltman 2010), but this did not improve the visualization in the case of 19 clusters. (See for more discussion about the differences between the two visualization techniques Leydesdorff and Rafols (2012).) However, the clustering algorithm in VOSviewer distinguished four, in our opinion highly meaningful, groups (Waltman et al. 2010). The organization into these four groups (biomedical, physical, environmental, and social sciences) is now provided as another (optional) partition within the Pajek (.paj) file containing the base map, and is also made available as input to VOSviewer.
- 1.Within the WoS (v. 5.5), one can “Analyze Results” by clicking at the right top of the page with search results; choose “Web of Science Categories” among the ranking options, and export the data into a file “analyze.txt”. This file can be read by the program wc10.exe, and the resulting file “wc10.vec” can be imported into the base map as a vector.1 The visualization (Draw-Partition-Vector within Pajek) then shows the overlay (e.g., Fig. 1).
- 2.The routine wc10.exe also generates three so-called “map”-files for VOSviewer: vos4.csv, vos6.csv, and vos19.csv. (The csv-extension makes these text files also readable using Excel.) These files generate maps when read into VOSviewer with four, six, and 19 clusters, respectively (using different colors). The manual of VOSviewer can be consulted for further options (Fig. 2).
A PowerPoint file is provided at http://www.leydesdorff.net/overlaytoolkit/basemaps.pptx which allows the user to place the legends on top of the maps and which provides a few examples; these legends can also be edited. An additional routine enables the user to measure Rao-Stirling diversity as an index of the interdisciplinarity in the samples under study (cf. Carley and Porter 2012; Leydesdorff and Rafols 2011; Porter and Rafols 2009; Rafols et al. 2012; Stirling 2007).
By thus adjusting to the new situation, we hope to have provided the community with a means to map inter- and multidisciplinary sets of documents in future research using the new version of the Web of Science (cf. Leydesdorff and Rafols 2009; Melkers and Hicks 2012; Porter and Youtie 2009; Soós and Kampis 2011). A detailed manual for the mapping was provided (at the website) by Ken Riopelle. Additionally, a macro to transform the file “analyze.txt” into the Gephi format was provided by Clement Levallois.
We are grateful to Alan Porter for comments on a previous draft. We acknowledge Thomson Reuters for the use of the data. We acknowledge support from the ESRC grant RES-360-25-0076.
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