Buckinghamshire is a county of south-eastern England, located north west of London. It is bordered by Greater London, Berkshire, Oxfordshire, Northamptonshire, Bedfordshire and Hertfordshire. The county town is Aylesbury. Buckinghamshire consists of three distinct zones: a belt of commuter towns (such as High Wycombe, Beaconsfield, Chesham, Amersham and Chorleywood) in low-lying or undulating terrain closest to London; the Chiltern Hills, a chalk ridge running SW-NE across SE England which is heavily wooded and scored by numerous steep-sided valleys; and Aylesbury Vale, an agricultural plain NW of the Chiltern escarpment. The new city of Milton Keynes lies in the north of Buckinghamshire (since 1996 this has been a Unitary Authority outside the administrative county).