The Seoul Metropolitan Area refers to the administrative districts of Seoul Special City, Incheon Metropolitan City, and Gyeonggi-do. This area occupies 11.8% of the total land area and has developed rapidly with the growth of the capital Seoul. As of 2021, it has 28 cities, accounting for a third of all 77 cities of the country. There are only five -gun districts, which are classified as rural areas: Yeoncheon-gun, Gapyeong-gun, and Yangpyeong-gun in Gyeonggi-do and Ganghwa-gun and Ongjin-gun in Incheon Metropolitan City. Therefore, the Seoul Metropolitan Area is mostly an urbanized area.

Most of the Seoul Metropolitan Area belongs to the Hangang river basin. Hwacheon Dam, Soyanggang Dam, Chungju Dam, and Paldang Dam provide abundant water resources and electricity to the Seoul Metropolitan Area. As of 2021, there were five wide-area water supply networks for the metropolitan area: four networks using Paldang Dam as the water intake source and the Ilsan wide-area water supply network using the Hangang intake source for Goyang-si and Paju-si. These networks provide a stable water resource supply system throughout the metropolitan area. In addition, the sewage treatment system and sludge treatment facilities have developed along with rapid urbanization.