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.

Seoul, officially the Seoul Special City, is the capital and largest metropolis of South Korea. Seoul has a population of 9.7 million people, and forms the heart of the Seoul Capital Area with the surrounding Incheon metropolis and Gyeonggi province.