然公園都道府県別面積総括自 [General overview of area figures for Natural Parks by prefecture] (PDF) (in Japanese). Ministry of the Environment. 31 March 2019. Retrieved 3 August 2019.
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books.google.ge
Nussbaum, Louis-Frédéric. (2005). "Kumamoto prefecture" in Japan Encyclopedia, p. 572, p. 572, at Google Books.
Nussbaum, "Kumamoto" in p. 572, p. 572, at Google Books.