TANIMURA, S.; KUROIWA, C.; MIZOTA, T. . 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: 30 nov. 2021.