“ Four seas measurement” in the Yuan dynasty is the latitude surveying in ancient China,namely astronomical surveying or astronomical geodetic surveying. The combined survey for the islands and reefs in the South China Sea research in the 20^Th century is not only the innovation project of marine research in China, but also the first ever marine geodetic survey in the South China Sea. The paper overviews the “four seas measurement” and the “combined survey for the islands and reefs”, and juxtaposes the ancient South China Sea survey points calculated by professor Han Zhen-hua and the contemporary geographical position of Huangyan Island on the same picture, which provides a precise and reliable scientific basis for the research and verification of the South China Sea survey points in the “four seas measurement”.

four seas measurement    combined survey for the islands and reefs    surveying and mapping    astronomical surveying    the South China Sea    the South China Sea Islands    Huangyan Island