Hong Kong is renowned for its expansive skyline and deep natural harbor. With a land mass of 1,104 km2 (426 sq mi) and a population of seven million people, Hong Kong is one of the most densely populated areas in the world. Hong Kong runs on economic and political systems different from those of mainland China. Hong Kong is one of the world's leading international financial centers, with a major capitalist service economy characterized by low taxation, free trade and minimum government intervention under the ethos of positive non-interventionism. The Hong Kong Stock Exchange is the sixth largest in the world, with a market capitalization of US$2.97 trillion as of October 2007. In 2009, Hong Kong raised 22% of worldwide IPO capital, making it the largest center of initial public offerings in the world. Hong Kong's currency is the Hong Kong dollar, which has been pegged to the U.S. dollar since 1983.