The world's megacities, from Tokyo to New York, are incredibly influential, housing vast swaths of the population and contributing significantly to global GDP.

But smaller cities and cities in emerging markets are also establishing themselves as globally competitive, and some, like Ahmedabad in India and Tianjin in China, are experiencing double-digit economic growth.

Citigroup has a new ranking of the world's most competitive cities, taking into account everything from economic size and growth to business and regulatory environment, quality of human capital, and quality of life.

A few major takeaways from the report:

Cities in the U.S. and Europe are still the most competitive , despite concerns about aging infrastructures and budget deficits. They're still the best at attracting capital, business, talent, and tourists.

, despite concerns about aging infrastructures and budget deficits. They're still the best at attracting capital, business, talent, and tourists. Asian cities dominated the "economic strength" section of the index. Fifteen of the top 20 cities by that measure are in Asia, a reflection of Asia's overall economic rise.

of the index. Fifteen of the top 20 cities by that measure are in Asia, a reflection of Asia's overall economic rise. T he biggest advantage for cities in developed countries is their ability to attract and develop talent . Another plus for cities in the U.S. and Europe, thanks to their on their high-quality education systems and "entrepreneurial mindset" of citizens.

. Another plus for cities in the U.S. and Europe, thanks to their on their high-quality education systems and "entrepreneurial mindset" of citizens. There is a correlation between density and competitiveness. Urban density is linked to higher productivity, while there is no connection between the size of a city's population and its competitiveness on the index.

We've picked out a few key categories from the report to highlight the world's most competitive cities.