Territorial authorities are the second tier of local government in New Zealand, below regional councils. There are 73 territorial authorities: 16 city councils, 56 district councils, and the Chatham Islands Council. Five territorial authorities (Nelson City Council, Gisborne, Tasman, and Marlborough District Councils and the Chatham Islands Council) also perform the functions of a regional council and thus are known as unitary authorities. Territorial authority districts are not subdivisions of regions, and some of them fall within more than one region. Taupo District has the distinction of straddling the boundaries of four different regions (see below). Regional council areas are based on water catchment areas, whereas territorial authorities are based on community of interest and road ac