Dunedin is the second-largest city in the South Island of New Zealand, and the principal city of the Otago Region. It is considered to be one of the four main urban centres of New Zealand for historic, cultural, and geographic reasons. Dunedin was the largest city by territorial land area until superseded by Auckland on the creation of the Auckland Council in November 2010. Dunedin was the largest city in New Zealand by population until about 1900. The Dunedin urban area lies on the central-eastern coast of Otago, surrounding the head of Otago Harbour. The harbour and hills around Dunedin are the remnants of an extinct volcano. The city suburbs extend out into the surrounding valleys and hills, onto the isthmus of the Otago Peninsula, and along the shores of the Otago Harbour and the Pacific Ocean.