Localities, also called urban sub-divisions, are component areas of the urban areas (conurbations) of England and Wales defined by the Office for National Statistics to enable detailed study of smaller areas within conurbations, and to enable comparisons to be made with historical data. The boundaries of localities within conurbations often follow those of local authorities existing before local government re-organisation in 1974, the boundaries of current authorities within agglomerations, or the points where previously separate urban areas joined.