LOECHER, M.; ROPKINS, K. RgoogleMaps and loa: Unleashing R Graphics Power on Map Tiles. Journal of Statistical Software, [S. l.], v. 63, n. 4, p. 1–18, 2015. DOI: 10.18637/jss.v063.i04. Disponível em: https://www.jstatsoft.org/index.php/jss/article/view/v063i04. Acesso em: 18 jan. 2022.