Japan consists of four main islands - Honshu, Hokkaido, Shikoku, and Kyushu. Population densities are highest in the lowland areas of these islands where farming is most productive and there are larger cities/industrial areas. Densities are lowest in the mountainous interiors due to unfavorable conditions for agriculture, short growing seasons, high rainfall, and lack of infrastructure/jobs. Specifically, the mountainous areas have steep terrain, thin soils, cold winters, and cool summers that limit food production.