Introduction Maps of science are an effective technique, especially for non-experts, to facilitate intuitive understanding of science activities, even though they could be cut both ways. Among such maps, science overlay maps have received adequate attention from scientometrics researchers (PerianesRodríguez et al., 2011; Grauwin & Jensen, 2011; Klaine et al., 2012; Leydesdorff, Rotlo, & Rafols,...