Ten-dash line

The ten-dash line is a cartographic boundary depicted on official maps published by the People's Republic of China that encloses the vast majority of the South China Sea, including the Paracel Islands, Spratly Islands, Scarborough Shoal, and the Pratas Islands. It is an extension of the earlier nine-dash line, which originated from a 1947 map produced by the Republic of China (then governing the mainland) that originally featured eleven dashes. After 1949, the PRC inherited and modified the line, eventually adding a tenth dash east of Taiwan in a 2013 vertical map published by Hunan Map Press, emphasizing that Taiwan falls within the same claim envelope.

China has never formally clarified whether the line represents a claim to all waters within it, only to the land features and their adjacent maritime zones, or a looser "historic rights" claim. This ambiguity is central to the dispute. Rival claimants include Vietnam, the Philippines, Malaysia, Brunei, and Taiwan, each asserting overlapping sovereignty or maritime entitlements under the UN Convention on the Law of the Sea (UNCLOS).

In July 2016, an arbitral tribunal constituted under Annex VII of UNCLOS, ruling in Philippines v. China, found that China's claims to "historic rights" within the nine-dash line had no legal basis under UNCLOS to the extent they exceeded entitlements derived from land features. China rejected the ruling and continues to publish the line on official maps.

In August 2023, China's Ministry of Natural Resources released a "standard map" featuring the ten-dash line, prompting formal protests from the Philippines, Vietnam, Malaysia, Indonesia, and India (the latter over a separate boundary depiction). The line remains a flashpoint in regional security, undergirding incidents around Second Thomas Shoal, Scarborough Shoal, and Vanguard Bank, and shaping freedom-of-navigation operations conducted by the United States and allies.