Note:  Do not rely on this information. It is very old.

Yezo

Yezo, Yesso, or Jesso, also called Matsmai, the most northerly of the islands of Japan, separated from Niphon by the Strait of Sangar, and from Saghalien by that of La Perouse. It has an area of about 62,500 square miles, being traversed from N. to S. by rugged mountains, mostly volcanic, but having fertile plains in the N.