London is the capital and largest city of England and the United Kingdom. The city stands on the River Thames in the south-east of England, at the head of its 50-mile (80 km) estuary leading to the North Sea. The City of London, London's ancient core and financial centre − an area of just 1.12 square miles (2.9 km2) and colloquially known as the Square Mile − retains boundaries that closely follow its medieval limits.

Washington, D.C., formally the District of Columbia and also known as D.C. or Washington, is the capital city of the United States of America. Located on the Potomac River bordering Maryland and Virginia, the city is one of the most visited cities in the United States, with more than 20 million visitors annually.