Individual buildings “of special architectural or historic interest” have enjoyed a means of statutory protection since the 1950s, but the concept of protecting areas of special merit, rather than buildings, was first brought under legislative control with the passing of the Civic Amenities Act in 1967. A crucial difference between the two is that listed buildings are assessed against national criteria, with lists being drawn up by the government with advice from English Heritage. Conservation Areas, by contrast, are designated by local authorities on more local criteria, and they are therefore very varied - small rural hamlets, mining villages, or an industrial city centre. However, general guidance on the designation of Conservation Areas is included in Planning Policy Guidance Note 15 (PPG15), which sets out the government’s policies on the historic built environment in general. By 2005, the London Borough of Hackney had designated 22 conservation areas.