The findings were made after property consultancy Knight Frank looked into the most important cities in terms of where the world's wealthy live, invest, educate their children, grow their businesses and spend their leisure time.
London came top in the study, marking the second year in a row that it has beaten New York in Knight Frank's Wealth Report, with Singapore, Hong Kong and Paris also making the top 10 list.
The research looked at how easily accessible cities are in terms of flight time for ultra-high-net-worth individuals - defined as those who have a net worth of £21.5 million-plus.
It found that Paris is the best-connected city for the mega-rich population, with more than 16,900 people in this bracket living within two hours of the city.
Although New York has the most ultra-high-net-worth residents, London's geographical position means that within a two-hour flight time the city is accessible to more than 16,000 ultra-wealthy people, compared with New York's 8,300.
The report said the concentration of wealth within Europe pushes cities in the region higher up the rankings in terms of accessibility.
Knight Frank said there are now around 187,500 ultra-high-net-worth individuals around the world, down from 193,100 in 2014.
Liam Bailey, head of research at Knight Frank, said: "London and New York's positions at the top of our survey results look invincible for the immediate future due to their long-established lead over other cities.
"However, further down the leader board the main battleground is Asia, where our respondents predict that Shanghai will eclipse Hong Kong's position, in terms of its importance to the wealthy over the next 10 years."
Here are the most important cities for the ultra-wealthy in 2016, according to Knight Frank:
2. New York
4. Hong Kong