In 1974 a new two-tier system of counties and districts was established across England and Wales.
Six of the upper-tier units, all in England and representing heavily built-up areas (other than Greater London), were designated 'metropolitan counties' and were subdivided into 'metropolitan districts'.
As with non-metropolitan areas the respective authorities covered all areas of local government, but the distribution of responsibilities was different to that of the county/local authority district structure.
In 1986 the metropolitan county councils were abolished, although the county areas are still recognised, especially for statistical purposes.
The 36 metropolitan district councils were left as single-tier authorities, a status retained to date, and accordingly have more powers than their non-metropolitan local authority district (LAD) equivalents.
Metropolitan districts are subdivided into electoral wards.
On 1 January 2011, the GSS Coding and Naming Policy was implemented. This policy led to the creation of a new, 9 character, coding system for all geographies held by ONS. For further information, please refer to the Code History Database (CHD).