This is the definitive set of regional council boundaries for 2006 as defined by the Local Government Commission and/or regional councils themselves but maintained by Statistics New Zealand (the custodian) as at 1 January 2006. The regional council is the top tier of local government in New Zealand. There are 16 regional councils in New Zealand (defined by Part 1 of Schedule 2 of the Local Government Act 2002). Eleven are governed by an elected regional council, while five are governed by territorial authorities (the second tier of local government) who also perform the functions of a regional council and are known as unitary authorities. These unitary authorities are Nelson City Council, and Gisborne, Tasman, and Marlborough District Councils. The Chatham Islands Council also performs some of the functions of a regional council, but is not strictly a unitary authority. Unitary authorities act as regional councils for the purposes of a wide range of legislative purposes. Regional councils are responsible for the administration of many environmental and transport matters such as land transport planning and harbour navigation and safety. Regional Councils were established in 1989 after the abolition of the 22 local government regions. The Local Government Act 2002 requires the boundaries of regions to conform, as far as possible, to one or more water catchments. When determining regional boundaries, the Local Government Commission gave consideration to regional communities of interest when selecting which water catchments to include in a region. It also considered factors such as natural resource management, land use planning and environmental matters. Some regional council boundaries are coterminous with territorial authority boundaries but there are several exceptions. An example is Taupo District, which is geographically split between four regions, although most of its area falls within the Waikato Region. Where territorial local authorities straddle regional council boundaries, the affected area is statistically defined by complete area units. In general, however, regional councils contain complete territorial authorities. The seaward boundary of any coastal regional council is the twelve mile New Zealand territorial limit.