地理院タイルを背景図に使用しています．
「The bathymetric contours are derived from those contained within the GEBCO Digital Atlas, published by the BODC on behalf of IOC and IHO (2003) (https://www.gebco.net/) 海上保安庁許可第292502号（水路業務法第25条に基づく類似刊行物）」
Shoreline data is derived from: United States. National Imagery and Mapping Agency. "Vector Map Level 0 (VMAP0)." Bethesda, MD: Denver, CO: The Agency; USGS Information Services, 1997.