Megalopolis

Megalopolis is defined as;
A megalopolis (or megapolis) is defined as an extensive metropolitan area or a long chain of roughly continuous metropolitan areas.

This is only a 4th floor view but it is pretty easy to see that all you see around you is buildings.

In Japan it is also noted as these areas;
The megalopolis of the Pacific coast is connected from the Greater Tokyo to Kyushu by the Shinkansen and the highway. The distance is 1,200km and is called the Taiheiyo Belt.

Taiheiyō Belt : Ibaraki, Saitama, Chiba, Tokyo, Kanagawa, Shizuoka, Aichi, Gifu, Mie, Kyoto, Osaka, Hyogo, Wakayama, Okayama, Hiroshima, Yamaguchi, Fukuoka, and Oita. (roughly 82.9 million)

Reffrence Wikipidia