According to 1991 population estimates, which city of the world has the largest population, 27 million in its metro area?

While city rankings constantly shift, the early 1990s saw one metropolitan area eclipse all others in sheer size. The designation of Tokyo/Yokohama as the world's most populous region was based on the concept of an urban agglomeration, where distinct cities grow so large that they merge into a single, continuous urban sprawl. Fueled by decades of a booming post-war economy, the Greater Tokyo Area, which includes the major port city of Yokohama and other surrounding municipalities, had swelled to an incredible 27 million residents by that time.

This immense concentration of people was a direct result of Japan's economic miracle, which peaked in the late 1980s. The Kanto Plain, where these cities are located, became the nation's undisputed economic, political, and cultural hub, drawing millions from across the country for work and opportunities. The cities are bound together by one of the world's most extensive and efficient commuter rail networks, allowing them to function as a single, integrated megacity. Even today, the Greater Tokyo Area remains one of the most populous urban regions on the planet, a testament to the massive growth it experienced in the 20th century.