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 Arla family relocated from B'hal Ta to New Sydney. Arla Rees was born here. (DS9 - Millennium novel: The Fall of Terok Nor).
New Sydney is also the birthplace of Ezri Tigan, and still home to the Tigan family, who own a large mining consortium on the planet. (DS9 episode: "Prodigal Daughter")
Liam Bilby's wife Morica and their children lived there in the 2370s. (DS9 episode: "Honor Among Thieves")