The Oshima Peninsula (渡島 半島 Oshima-hantō) is the southernmost part of Hokkaidō, the northernmost of the Japanese islands. Where the peninsula starts is open to interpretation. A more generous interpretation is to draw a line southeast from Ishikari Bay across the Ishikari Plain to Yufutsu. A narrower interpretation is to draw a line connecting Suttsu on the Sea of Japan and Oshamambe on Uchiura Bay. This narrow interpretation encompases the subprefectures of Oshima and Hiyama.