Pishgahifard, Zahra, and Hassan Salehi. “Geo-Economics and Considerations on the Tourism Industry With Emphasis on Historical Cities Tourism and Ecotourism in Iran”. International Journal of Sciences: Basic and Applied Research (IJSBAR), vol. 15, no. 1, Apr. 2014, pp. 301-10, https://www.gssrr.org/JournalOfBasicAndApplied/article/view/2155.