Anna, Z., P. Hindayani, and I. A. P. Putri. “Indonesian Cities Green Development Index: A Prototype Measurement”. International Journal of Sciences: Basic and Applied Research (IJSBAR), vol. 37, no. 3, Apr. 2018, pp. 290-08, https://www.gssrr.org/index.php/JournalOfBasicAndApplied/article/view/8883.