Japan is an island country off the coast of mainland Asia, just a few hundred miles away from Russia, China, and Korea. The four major islands - Hokkaido, Honshu, Shikoku, and Kyushu - form a curve that extends about 1,200 miles. About 125 million people live on these islands making it one of the most densely populated countries. Much of the country is covered in mountains and hills, so about 90 percent of the population lives on the coastal plains which account for about 20 percent of the land area..