The city includes two controversial island chains – the Paracels and Spratlys, known as the Xisha and Nansha Islands respectively in Chinese – and an underwater atoll.

The Ministry of Natural Resources released an updated map of the city on Sunday showing the labels of Xisha and Nansha districts, which were created in 2020 but did not appear on previous maps.

Sansha, part of the southern island province of Hainan, was established in 2012 to assert China’s claims to the resource-rich South China Sea.

The Ministry of Civil Affairs also assigned administrative region identifiers to the two districts. These codes are used to identify places for census and administrative purposes and generally appear as the first six digits on the identity cards of residents born and registered in an area.

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History, money and military: why the South China Sea is so important to Beijing

History, money and military: why the South China Sea is so important to Beijing

Separately, China Post announced on Sunday that postal codes had been granted to Nansha District, while three inhabited islands in Xisha District – Woody Island, Tree Island and Jinqing Island – would continue to use their respective codes.