“…In this sense, classification systems are an indispensable tool to study the structure and dynamics of scientific fields (Boyack, Klavans, & Börner, 2005;Glanzel & Schubert, 2003;Leydesdorff, Carley, & Rafols, 2013;Leydesdorff, de Moya-Anegón, & Guerrero-Bote, 2014;Ruiz-Castillo & Waltman, 2015;Y. Zhu & Yan, 2015;Waltman & van Eck, 2012;Zitt, 2015).…”