South Korea is surrounded by the sea on its three sides, and the sea has long been the base of opportunities to offer human beings something to see, eat, and work with. Development spurred by rapid industrialization, however, drove human beings to the limited utilization of land whose area was not infinite. Now people are turning to the ocean with infinite potential and possibilities for development. It is not an issue taking place only in South Korea. There have been often dominium cases over the sea between neighboring nations, and South Korea is no exception. There has been a cadastre system for land for many years. The public authorities investigate and survey the solid activities and current states of land, register the data in the public registers fit for the new digital environment, and make it sure that the territories and ownership protection are managed in a systematic fashion. The reality of the ocean is, however, different even though it has infinite possibilities and grows in its importance day after day. There is no systematic management of the ocean due to the absence of management systems and devoted management departments. It has been several years since they started to conduct active researches on marine cadastre. The introduction of a marine cadastre system needs a few requirements including the setting of categories of the sea like the categories of land, the categorization of the sea by the uses, the registration of marine boundaries based on precise marine surveys with UAV, for instance, and the establishment of public registers to manage them systematically and register all kinds of rights. The first step would involve setting the categories of the sea, building a foundation for a marine cadastre system, and managing a marine cadastre efficiently, which led to the present study. The current categories of land have very limited functions and roles due to the diversification and complexation of land uses according to the changing social and economic environments, frequent alterations of uses, and poor legal and institutional improvements. Since the current law restricts the categories of land to 28, they will face limits in encompassing even the information of marine spaces whose values and importance grow bigger and bigger every day. With its findings, the present study will make even the slightest contribution to the establishment of a marine cadastre system by setting the categories of the sea for more efficient and systematic management of the ocean. It is time to make preparations for the upcoming maritime age by establishing an efficient government-led management system for marine spaces through thorough surveys.