Milton Keynes is a city in Buckinghamshire, England, about 50 miles (80 km) north-west of London. At the 2021 Census, the population of its urban area was 264,349. The River Great Ouse forms the northern boundary of the urban area; a tributary, the River Ouzel, meanders through its linear parks and balancing lakes. Approximately 25% of the urban area is parkland or woodland and includes two Sites of Special Scientific Interest (SSSIs).