At present, the Yangtze River delta and Pearl River delta areas are the most fully developed, followed by the Beijing–Tianjin–Bohai Bay cluster and the recently initiated Northeast cluster (Table 1). The Pearl River delta city cluster has expanded rapidly since the 1980s, due primarily to former political leader Deng Xiaoping's policy of creating “special economic zones”, designated regions where governmental policy fosters a market economy instead of a planned economy. Similarly, the exponential economic growth of Shanghai in the 1990s led rapidly to accelerated growth among cities in its neighborhood. The Beijing–Tianjin–Bohai Bay area is a unique city cluster that formed spontaneously around the twin megacities of Beijing and Tianjin.