Design and update of a classification system : the UCSD map of science
Article [Version of Record]
Abstract(s)
Global maps of science can be used as a reference system to chart career trajectories, the location of emerging research
frontiers, or the expertise profiles of institutes or nations. This paper details data preparation, analysis, and layout performed
when designing and subsequently updating the UCSD map of science and classification system. The original classification
and map use 7.2 million papers and their references from Elsevier’s Scopus (about 15,000 source titles, 2001–2005) and
Thomson Reuters’ Web of Science (WoS) Science, Social Science, Arts & Humanities Citation Indexes (about 9,000 source
titles, 2001–2004)–about 16,000 unique source titles. The updated map and classification adds six years (2005–2010) of WoS
data and three years (2006–2008) from Scopus to the existing category structure–increasing the number of source titles to
about 25,000. To our knowledge, this is the first time that a widely used map of science was updated. A comparison of the
original 5-year and the new 10-year maps and classification system show (i) an increase in the total number of journals that
can be mapped by 9,409 journals (social sciences had a 80% increase, humanities a 119% increase, medical (32%) and
natural science (74%)), (ii) a simplification of the map by assigning all but five highly interdisciplinary journals to exactly one
discipline, (iii) a more even distribution of journals over the 554 subdisciplines and 13 disciplines when calculating the
coefficient of variation, and (iv) a better reflection of journal clusters when compared with paper-level citation data. When
evaluating the map with a listing of desirable features for maps of science, the updated map is shown to have higher
mapping accuracy, easier understandability as fewer journals are multiply classified, and higher usability for the generation
of data overlays, among others.