A little history here.  In 1946 after the Japanese occupation in the South China Sea, China claimed sovereignty over a 11 dash line drawn in the SCS encompassing some 120,000 square kilometers.  In 1954 the Chinese adjusted to a 9 dash line to pacify the Vietnamese on some islands.  At the time there was little interest to contest this land grab since most of the islands were little more than uninhabited atolls.  But today in the rush for oil and gas exploration there is a challenge to this questionable claim of the high seas by China.