) and a population of seven million people, Hong Kong is one of the most densely populated areas in the world.Under the principle of "one country, two systems", Hong Kong has a different political system from mainland China. Hong Kong's independent judiciaryfunctions under the common lawframework. Hong Kong Basic Law, its constitutional document, which stipulates that Hong Kong shall have a "high degree of autonomy" in all matters except foreign relations and military defence, governs itspolitical system..
Hong Kong is a world city. It is one of the Alpha+ cities. Also, a Time Magazine article in 2008 coined the phrase "Nylonkong", which referred to New York City, London and Hong Kong, that these three cities form a global network that facilitates the global economy. As Hong Kong ranks the third most important leading international financial centre, after London and New York City, Hong Kong has a major capitalist service economy characterised by low taxation and free trade, and the currency, Hong Kong dollar, is theeighth most traded currency in the world. The lack of space caused demand for denser constructions, which developed the city to a centre for modernarchitecture and the world's most vertical city. Hong Kong has one of thehighest per capita incomes in the world. The dense space also led to a highly developed transportation network with the public transport travelling rate exceeding 90 percent, the highest in the world. Hong Kong has numerous high international rankings in various aspects. For instance, its economic freedom, financial and economic competitiveness, quality of life, corruption perception,Human Development Index are all ranked highly. According to estimates from bothUN and WHO, Hong Kong had the longest life expectancy of any region in the world in 2012. Hong Kong also has the highest average IQ score in 81 countries around the world.