The Planning (Listed Buildings and Conservation Areas) Act 1990 requires local authorities to designate as conservation areas any areas of special architectural or historic interest the character or appearance of which it is desirable to preserve or enhance. Guidance on the assessment and designation of conservation areas is included in Planning Policy Guidance Note 15 (Planning and the Historic Environment). This says that the prime consideration in identifying conservation areas should be the quality and interest of areas, rather than that of individual buildings. It also says that cancellation of designation should be considered where an area or part of an area is no longer considered to possess the special interest which led to its original designation.