Abstract: The 11th Five-Year Plan (2006-2010) states that city agglomerations should be regarded as the main form of urbanization, and the 12th Five-Year Plan (2011-2015) puts more emphasis on improving the structure of city agglomerations to promote urbanization in China. It means that city agglomerations have been and will still be the major region into which the population and other economic elements concentrate in China. More importantly, the spatial structure of city agglomerations would have an important influence on the quality and level of urbanization through affecting economic performance. This article aims to examine the clustering of China's urban agglomerations and find out the relationship between economic clustering and growth rate of urban agglomerations. Our data are obtained from Gross Domestic Production (GDP) and population statistics of 20 urban agglomerations of China from 1995 to 2010. The conclusions can be obtained as follows. (1) Generally speaking, it is evident that the degree of clustering of urban agglomeration has been ever increasing in the past several years. Although there is a relatively large gap in the degree of concentration between population and economy, the data shows a strong positive linear correlation between them. (2) The 20 city agglomerations can be classified into four groups according to their clustering characteristics. Gini indices and the proportion of GDP of primary city are employed to detect the clustering characteristics of city agglomerations. As a result of investigation, four groups include strong singe-center clustering; multi-centers clustering; weak singe-center clustering and weak centers clustering. (3) As the relationship between clustering of population and growth rate is still unclear, there exists an obvious inverted-U-shaped relationship between economic clustering and growth rate of urban agglomerations. The result further indicates that when Gini indices of GDP in large and medium-sized urban agglomerations are about 0.2 and the primary city's proportion of GDP in small urban agglomerations is about 65%, the fastest growth rate can be achieved in China.

Key words: population and economic clustering, urban agglomeration, economic growth