Like several New Zealand centres, it was officially designated a city until administrative reorganisation in 1989, and is now run by a District Council. Although the city was called Wanganui from 1854, in February 2009, the New Zealand Geographic Board recommended the spelling be changed to "Whanganui". In December 2009, the government decided that while either spelling was acceptable, Crown agencies would use the Whanganui spelling.
On 17 November 2015, Land Information New Zealand (LINZ) announced that Wanganui District would be renamed to Whanganui District. This changed the official name of the District Council, and, because Whanganui is not a city but a district, the official name of the urban area as well.
Whanganui is located on the South Taranaki Bight, close to the mouth of the Whanganui River. It is 200 kilometres north of Wellington and 75 kilometres northwest of Palmerston North, at the junction of State Highways 3 and 4. Most of the city lies on the river's northwestern bank, due to the greater extent of flat land. The river is crossed by four bridges – Cobham Bridge, City Bridge, Dublin Street Bridge and Aramoho Railway Bridge (rail and pedestrians only).