The farmland west of Buckingham Palace became residential after 1820. The developer was Lord Grosvenor and the builder was Thomas Cubitt. The name Belgravia came from a village on the Grosvenors' Leicestershire estate. It is not an administrative district - but it is one of London's most fashionable areas, famous for its gleaming white terraces, dark green foliage and secluded gardens. Belgravia lies between Buckingham Palace Road, Pimlico Road and Sloane Street, partly in Kensington and partly in Chelsea. Large houses with large gardens cost over £10 million. Belgravia Square is an exclusive key-holder garden of 4.5 acres surrounded by embassies and diplomatic residences. Many large Belgravia properties (eg round Eaton Square) have been converted to apartments and their residents can spend summer afternoons relaxing in large gardens which they do not have to maintain.
For historical information on Belgravia, see Muirhead's 1927 London Walks:
Eaton Square, Belgravia, London
Belgravia window boxes, London
Eaton Square gardens