They didn't label everything. According to their research paper (http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjourna...) they covered the "natural sciences, social sciences, as well as the humanities." From the companion article (http://www.lanl.gov/news/index.php/fuseaction/home.story/sto...) "it's a graphic depiction of the virtual trails scientists leave behind when they retrieve information from online services."