Urban agglomeration is an important form of regionalized city development, but also an iconic product of advanced regional industrialization and urbanization. Based on the diverse conceptual evolution processes of urban agglomeration and focusing on the technical method s and approaches for the identification of urban agglomerations, this article reviews in detail the research progress of the range identification of urban agglomeration growth. It concludes that the main reasons that academia seldom reach consensus on the spatial extent of urban agglomeration are as follows: there exist significant differences in the understanding of the essence of the concept, definition, smallest unit of analysis, and choice of identification methods of urban agglomeration. This article clarifies the main research methods of range identification of urban agglomeration: (1) the traditional socioeconomic index method represented by defining metropolitan areas in the United States has broad influence and has set the fundamentals of range identification of urban agglomerations in the West; (2) applying gravity models for the recognition of the scope of influence of central cities has become the main method for urban agglomeration range identification research in China; (3) using spatial analysis technology in GIS as means, integrated simulation methods incorporating integrated indicators and modeling methods represent the future trend of study on the recognition and identification of urban agglomeration growth.

Recently, domestic and international economic situations have changed significantly. The Pearl River Delta (PRD) area in this period of transition is facing unprecedented challenges, and development strategies for the PRD need to be reconsidered. This article reviews the development process of the PRD and analyzes its development situation. Then, the PRD is compared with the urban agglomerations at home and abroad. The results show that in 2000-2013, the economic development and the population growth of the PRD have slowed down; the disparity of regional economic development has gradually narrowed; the industrial development tends to be more advanced; and economic globalization has decreased. At present, the level of development and competitiveness of the PRD is much weaker than world-class urban agglomerations. Compared with the Yangtze River Delta and the Beijing-Tianjin-Hebei Uban Agglomerations, the speed of development in the Pearl River Delta area has decreased. The PRD should attach greater importance to technology innovation of industries, intensification of land-use, innovation of population policy, regional cooperation, and humanistic concerns under the new conditions.

Urban agglomeration is an important carrier of China's new urbanization strategy, but also a new geographical unit for participating in global competition and international division of labor. At present, the mode of China's regional spatial governance is undergoing a major shift from the original spatial split according to the administrative divisions to govern in accordance with the type of area. Based on the significant extension of the characteristics of urban agglomerations, we divide the 23 Chinese urban agglomerations at four levels and analyze the spatial variation, aiming to provide a scientific basis for the implementation of China's urban agglomerations spatial pattern optimization and planning. First, the 23 areas are divided into national, regional, sub-regional and local levels of urban agglomerations with reference to the development status of more mature urban agglomerations worldwide, resulting in a "3-5-6-9" pyramid structure for the four levels. Then, based on the five essential characteristics of urban agglomerations, we build an index system for the classification of urban agglomerations that consists of 10 factors and 22 indicators, and a Q-type cluster analysis is employed to quantitatively group five kinds of the urban agglomerations: mature export-oriented type, dual-core catch-up type, environment-friendly type, single nuclear radiation type, and inland extensive type. Finally, by synthesizing the classification results of different levels and quantitative clustering, China's urban agglomerations are divided into 10 subgenera: National mature export-oriented genre, national dual-core catch-up genre, regional dual-core catch-up genre, sub-regional environment-friendly genre, local environment-friendly genre, regional single nuclear radiation genre, local single nuclear radiation genre, regional inland extensive genre, subregional inland extensive genre, and local inland extensive genre.

Delineating the scope of urban agglomerations is a basic condition for understanding the evolution of cities and regions and for developing strategies and planning of urban agglomerations. At present, the scope of urban agglomerations in China are mainly decided based upon analyses of center cities and their connections with other cities by viewing them as separate points, but there is few consensus on how to define the spatial boundary of urban agglomerations other than using the jurisdiction border of the cities. In practice, there is a tendency to take urban agglomeration as a policy tool for raising the importance of certain areas and promoting regional development. As a result, the number and scope of urban agglomerations have been exaggerated. In order to solve these problems, in this article a methodology for delineating the scope of urban agglomerations is discussed from an economic geographic perspective based on the 'Pole-Axis Theory'. A four-step process was proposed: (1) to make judgment of the existence of central cities; (2) to examine the cities' rank system and the resources and environment base of the region to see if an urban agglomeration can be sustained; (3) to analyze the social and economic connections between central cities and other cities in the region; (4) to evaluate the development level of urban agglomerations with the scale of 'Pole-Axis Theory'. A case study is conducted in the Beijing-Tianjin-Hebei Region, and a comparison is made about the formation and development of the five main urban agglomerations in the Beijing-Tianjin-Hebei, Yangtze River Delta, Perl River Delta, Middle Yangtze River, and Chengdu-Chongqing regions.

Regional research is one of the core topics of Geography. In the development process of geography, the debate on region is broadly divided into two categories—territorial space and network space—and there has been a trend of change from one-dimensional space to multidimensional space. Regions were often considered as a space that has one or more common features among its components, and a region is bounded, closed. With the advancement of globalization and information society, regional relations continue to strengthen. Therefore some scholars put forward the concept of network space, which highlights the interactions and relationships between regions. A network space is open, dynamic, and with uncertain boundaries. Increasingly, the single dimension to regional definition was viewed as biased. The space of Chinese urban agglomerations is a new type of region. It has multiple properties, not only as a territorial space and network space, but also as the place where space is produced and created. There is a great difference in perspective between territorial space and network space. Attention of regional research is shifting from production in space to the production of space itself. The production of space cannot take place without the operation of power, and space is also the product of the discourse construction. Based on the debates of a region as a territorial space, or a network space, and the production of space, this article discusses the debates on the concepts and construction of Chinese urban agglomerations. Taking the Zhongyuan urban agglomeration as an example, this research examined some practical problems in its construction, and addressed the vital question: What is an urban agglomeration and its nature? In order to coordinate and combine the varied dimensions on Chinese urban agglomeration, we put forward a TPSNF framework to integrate the five dimensions for defining urban agglomeration: territory, place, scale, network, and function and proposed some key research focus in the future.