Just as we can map the structure of science by clustering at the journal level, we can map the scientific literature at a finer grain by clustering at the level of individual articles using article citation data such as that available in the Microsoft collection. Again we use the Map Equation (Rosvall and Bergstrom 2008 Proc Nat Acad Sci USA). Because of the time-directedness of the article-level citation network, we treat this as an undirected graph. Recent developments (Bergstrom and Rosvall, unpublished) in clustering time-directed networks may further improve on the categorization presented here
Because the number of categories found in this way will be large, it is useful to turn to semantic labeling approaches to automatically assign names to categories and facilitate user navigation.