The discussion on Gimpo's incorporation into Seoul is developing into a discussion on the reorganization of the administrative system of Mega City. Is it really desirable for Seoul to incorporate Gimpo City from the perspective of the spatial structure of the city? Historically, the city has gradually expanded its sphere of influence, and the living area has been expanded to megapolis, urban conurbation, mega-regions, and ultra-wide areas. However, since administrative districts and hierarchical structures are different from country to country, there are various ways to resolve the inconsistency between living and administrative areas. In the case of Korea, there is a strong tendency to use radical metropolitan administrative measures such as merger or separation, which is largely influenced by the centralized local administration system. The living area of the residents of the metropolitan area has already expanded beyond Seoul, Gyeonggi-do, and even Chungcheong-do and Gangwon-do. Gyeonggi-do is insisting on a division and proposing the Incheon Special Self-Governing Province Plan, making it a difficult problem on how to resolve the conflict of regional discussions. The Seoul Metropolitan Government proposes the Korean-style Legion Plan as an alternative to respond to the Mega-region phenomenon.