Why do most people in Japan live in plains and lowlands along the Pacific coast?

The concentration of Japan's population in plains and lowlands along the Pacific coast is primarily driven by the country's rugged, mountainous terrain, which limits the amount of habitable land available. Because Japan lacks large, continuous structural plains, the population has naturally gravitated toward the few available low-lying areas, such as the Kantō Plain, where development is more feasible.123

This distribution has been further reinforced by historical and economic factors:

• Industrialization and Urbanization: Following the rapid industrial growth after 1950, major industrial districts—such as the Keihin, Keihanshin, and Chūkyō areas—expanded significantly along the Pacific seaboard. These regions, collectively known as the Pacific Belt Zone, became the primary hubs for employment and economic activity, drawing people away from rural, mountainous districts.14
• Historical Development: Many of Japan's major cities evolved from castle towns or port towns that were strategically located to control transportation routes and trade, most of which were situated on the Pacific side of the country.5

Consequently, these coastal lowlands now contain the majority of Japan's population and its largest cities.14