TANIMURA, Susumu; KUROIWA, Chusi; MIZOTA, Tsutomu. Proportional Symbol Mapping in R. Journal of Statistical Software, [S. l.], v. 15, n. 5, p. 1–7, 2006. DOI: 10.18637/jss.v015.i05. Disponível em: https://www.jstatsoft.org/index.php/jss/article/view/v015i05. Acesso em: 6 apr. 2025.