The shape of Japan (unless otherwise specified, Japan refers to the three major islands of Kyushu, Shikoku, and Honshu) is essentially linear with a maximum breadth about one-eighth of its length. In this paper, we analyse clines along the length of Japan using a one-dimensional model. https://www.jstage.jst.go.jp/article/ase1911/88/2/88_2_109/_pdf
