Accoording to the Wikipedia,

Hokkaidō is Japan's second largest island and the largest, northernmost of its 47 prefectural-level subdivisions. The Tsugaru Strait separates Hokkaidō from Honshū, although the two islands are connected by the underwater Seikan Tunnel. The largest city on Hokkaidō is its capital, Sapporo, which is also its only ordinance-designated city.


Contribution to Wikipedia Hokkaido

In the book on Page 194, Robinson explained as they were starting there fleet to Japan thw wind stopped which took them towards the Nipponese Island, past Hokkaido.