New Sydney is an independent mining colony located in the Sappora system. Due to the planet's independence from Starfleet and the Federation, the planet is influenced by the Orion Syndicate, and is the home of many nefarious races, such as the Ferengi and the Nausicaans.
Due to the Cardassian annexation of Bajor, the Bajoran Arla family relocated from B'hal Ta to New Sydney. Arla Rees was born on the planet. (DS9 - Millennium novels: The Fall of Terok Nor, The War of the Prophets)
The Romulan agent with the Vulcan identity of Seret knew of a species reconstruction specialist who lived on New Sydney, who was often used by the Orion Syndicate to surgically alter individuals to resemble other species. (DS9 - Tales of the Dominion War short story: "Mirror Eyes")