Ōshima is an uninhabited island in the Sea of Japan, 50 kilometers to the west from Matsumae town and therefore the westernmost point of Hokkaido. It is part of the town of Matsumae in Oshima Subprefecture in Hokkaido, Japan. To distinguish Ōshima from other islands with the same name, it is sometimes known as Oshima Ōshima or Matsumae Ōshi…Ōshima is an uninhabited island in the Sea of Japan, 50 kilometers to the west from Matsumae town and therefore the westernmost point of Hokkaido. It is part of the town of Matsumae in Oshima Subprefecture in Hokkaido, Japan. To distinguish Ōshima from other islands with the same name, it is sometimes known as Oshima Ōshima or Matsumae Ōshima.