Direct Citation Clustering of Science

Direct citation clustering maps the structure of science by linking publications through the citations that run directly between them and partitioning the resulting network into research areas. Unlike co-citation (which links papers cited together) or bibliographic coupling (which links papers sharing references), direct citation uses the citation itself as the edge: paper A is connected to paper B because A cites B. Kevin Boyack and Richard Klavans's 2010 comparison of citation approaches found that, at scale, direct citation can represent the research front at least as accurately as the alternatives, and Ludo Waltman and Nees Jan van Eck's 2012 methodology showed how to cluster very large direct-citation networks — millions of publications — into a coherent, publication-level classification of science using modularity-based community detection. Together these works established direct citation clustering as a leading technique for building large-scale science maps.