Guo Shoujing
In 1279, the Yuan dynasty emperor sent the high-level official and astronomer, Guo Shoujing, to the South China Sea to survey and measure the islands and the surrounding sea area. Guo's base of survey was claimed by China to be located in the Paracel Islands, although this is considered unlikely by many Chinese scholars. His activities were recorded in the "Yuan Shi", or History of Yuan. According to the "Yuan Shi", the South China Sea islands were within the boundary of the Yuan dynasty. Maps published in the Yuan era invariably included the "Changsha" (the Paracels) and the "Shitang" (the Spratlys) within the domain of Yuan.