Watercolour of one of London's most exclusive areas.
Grosvenor Square is a large garden square in the Mayfair district of Westminster, Greater London. It is the centrepiece of the Mayfair property of the Duke of Westminster, and takes its name from the duke's surname "Grosvenor". It was developed for fashionable residences in the 18th century. In the 20th it had an American and Canadian diplomatic presence, and currently is mixed use, commercial.
 
Interesting facts...
Grosvenor Square is that it was once known as “Little America”
From the 20th century on, the square hosted the U.S. Embassy (for decades in the Eero Saarinen‑designed building on the west side), as well as the American consulate and other American‑linked institutions.
The American link goes back even further: John Adams, the first U.S. Minister to the Court of St James’s and later the second U.S. president, lived in a house on Grosvenor Square