Abstract: Since the opening-up and reform from the late 1970s, the economic growth and transformation of urban morphology in the Pearl River Delta in Guangdong Province, China has drawn enormous attention. After over 30 years of rapid development in this region, it is needy to study the developmental processes and underlying mechanisms of the urban morphology evolution. Although the cities in the Pearl River Delta share similar market environment, their resource endowment and governance mode differ from the very beginning of development, resulting in different evolutionary paths of urban morphology. The top-down and bottom-up modes of governance both have been identified in the literature, which have exerted constant influences on urban development. Therefore, a comparative study of urban morphology change under the two governance modes is able to provide insights into the underlying dynamics behind the formation of urban morphology. Through the technical method of remote sensing and GIS, this paper reviews the evolution of urban morphology in six cities in the Pearl River Delta, i.e. Guangzhou, Shenzhen, Foshan, Dongguan, Zhongshan and Zhuhai. It depicts the spatialtemporal change of urban morphology at the city scale by combining such factors as economy, politics and planning, and summarizes the process and underlying forces of each city. Guangzhou, Shenzhen and Zhuhai are categorized under the top-down governance mode, while Foshan, Dongguan and Zhongshan are categorized under the bottom-up governance mode. The result suggests different evolutionary path of urban morphology in each city from 1979 to 2008 owing to specific geographic locations and institutional arrangements. Guangzhou, a city with industrial tradition in heavy industries, has formed a polycentric networked morphology with several big industrial conglomerates and investment of mass transit system. Shenzhen, as a special economic zone in China, has benefited from the investment of large state-owned and foreign companies, and the land use pattern has gone through rapid expansion and then to in-filled adjustment. Zhuhai, another special economic zone in the region, expanded eastward by large projects. Overall, the three cities under the top-down mode underwent relatively concentrated and in-filled land use expansion. On the other hand, Foshan, Dongguan and Zhongshan represent the bottom-up development mode, and their spatial morphologies are generally dispersal and scattered. Foshan and Zhongshan developed loosely in spatial terms in the beginning of the opening- up and reform, through the growth of specialized towns. Foshan, unlike Zhongshan, however, has seen strengthening connections between the clusters in the later phase of development in response to the increasing needs for Guang(zhou) Fo(shan) integration. Dongguan is very typical of the village-based economies, which is driven by overseas Chinese investment. Compared to the urban morphology pattern under the top-down governance mode, the bottom-up mode of urban expansion has given rise to the "road economy" and "village and township economy", which poses great challenges to the agglomeration economy and comprehensive environmental improvement. The importance of this inter-city spatial-temporal comparative study lies in the urgent need to understand the dynamism of urban morphology in contemporary China. By taking a perspective of governance mode, this paper may provide some references for policy makers in spatial restructuring of urban space in the future.

Key words: bottom-up mode, the Pearl River Delta, top-down mode, urban morphology