Chongqing is one of five National Central Cities in China. The populations of cities are difficult to measure as they grow more organically than countries without the constraints of borders. The Metropolitan Area includes those in the less populated commuter belt. For Chongqing, that includes 52.1 million people. The urban/rural definition is fuzzy and based on population density and infrastructure. Chongqing's has 36.7 million people. The 'City Proper' is more clearly defined by legal, or political, boundaries. By that definition, only 8.5 million people live there. In 1950, the world's urban population was just 746 million. By 2007, more than 50% of us were living in cities. The Chongqing municipality was created as a merger of 43 counties in order to spearhead China's western development.