The built-up areas of conurbations tend to cross historic county boundaries freely. Examples are Bournemouth–Poole–Christchurch (Dorset and Hampshire) Greater Manchester (Cheshire, Derbyshire, Lancashire and Yorkshire), Merseyside (Cheshire and Lancashire), Teesside (Yorkshire and County Durham), South Yorkshire (Yorkshire, Nottinghamshire and Derbyshire), Tyneside (County Durham and Northumberland) and West Midlands (Staffordshire, Warwickshire and Worcestershire). Greater London itself straddles five ancient counties — Essex, Hertfordshire, Kent, Middlesex, Surrey — and the London urban area sprawls into Buckinghamshire and Berkshire. The Local Government Act 1972 sought generally to unite conurbations within a single county, while retaining the historic county boundaries as far as was practicable.