7Gunn C A, Larsen T R. Illinois Zones of Tourism Potential. College Station, TX: A. T. Kearney Inc., Illinois Bureau of Tourism, 1993.
8Priskin J. Assessment of natural resources for nature-based tourism: The case of the Central Coast Region of Western Australia. Tourism Management, 2001, 22(6): 637-646.
9Margules C R, Usher M B. Criteria used in assessing wild- life conservation potential. Biological Conservation, 1981, 21(2): 79-109.
10Sherry R, Geoffrey W. Evaluating Ecotourism: The case of north Sulawesi, Indonesia. Tourism Management, 1999, 20(6): 673-682.