A Comparative Study Of Evolution And Spatial Economic Structure Typical Eastern Midwest City Group "polycentric

City agglomeration is the most mature form of cities, it’s product of both agglomeration and dispersion. Facing a series of urban problems of congestion, environment pollution and so on that brought by conventional single-center,"multicenter" becomes a significant and unique spatial economic structure and brings scholars’attention. Sufficient understanding of the inner spatial economic structure of city agglomeration is benefit to understand the development of city agglomeration and it’s inner single city more effectively and roundly.This paper analysis the spatial economic structure of cities agglomeration of the eastern,central and western regions, using typical location theory, regional economics theory and new economic geography theory. The paper educes the diversity of four cities agglomerations at frist, then analyses the spatial economic structure of city agglomeration from three angles that "form of multicenter","function of multicenter" and inner economic relation. At last, this paper analyses the endogenous mechanism of the proceeding of "multiple-center" spatial economic structure, and advises for achieving the "multicenter" of the eastern,central and western regions.The main conclusions are:first, four typical city agglomerations all appear "multicenter"-spatial economic structure; second, the four cities agglomerations don’t present polarization; third, the "multiple-center" spatial diversity of typical city agglomerations mainly shows between east region and middle region plus west region; forth, the level structure of the city agglomeration of the Yangtze River Delta region is more clearly, but also polarized feature becomes more obvious, while the cities in the city agglomeration of the Pearl River Delta region develop equally;fifth, the radiation range of the central and western cities agglomerations’ center is not enough,because of the small scale.