Japan is a country of over three thousand islands extending along the Pacific coast of Asia. The main islands, running from north to south, are Hokkaido, Honshu (the main island), Shikoku and Kyushu. The Ryukyu Islands, including Okinawa, are a chain of islands south of Kyushu. Together they are often known as the Japanese Archipelago.

About 70% to 80% of the country is forested, mountainous, and unsuitable for agricultural, industrial, or residential use. This is because of the generally steep elevations, climate and risk of landslides caused by earthquakes, soft ground and heavy rain. This has resulted in an extremely high population density in the habitable zones that are mainly located in coastal areas. Japan is the thirtieth most densely populated country in the world.

Its location on the Pacific Ring of Fire, at the juncture of three tectonic plates, gives Japan frequent low-intensity tremors and occasional volcanic activity. Destructive earthquakes, often resulting in tsunamis, occur several times each century. The most recent major quakes are the 2004 Chuetsu earthquake and the Great Hanshin Earthquake of 1995. Hot springs are numerous and have been developed as resorts.
 

Reference
http://en.wikipedia.org/wiki/Japan#Geography