Review of the Methods of Delimitation for the Spatial Scope of Urban Agglomeration

Transcription

1 Review of the Methods of Delimitation for the Spatial Scope of Urban Agglomeration Jian Liang 1 Feixue Li* 1 Liang Mao 2 1 School of Geographic and Oceanographic Science, Nanjing University, Nanjing , P. R. China; 2 Department of Geography, State University of New York at Buffalo, Buffalo, NY 14261, USA *Corresponding author, njulifeixue@163.com Abstract the delimitation of urban agglomeration region is a critical issue in urban studies. But there are no standard methods so far for the delimitation. Starting with the concept of urban agglomeration, this paper reviews the methods of the delimitation of urban agglomeration region. We sum up two types of the methodology of the delimitation of urban agglomeration region. We compare and analyze a variety of promising and representative methods such as the key indicators distribution analysis, radiant ability of central city-based analysis, modeling analysis, multi-factor overlay analysis and spatial correlation analysis. Based on such, the common characteristics of the existing methods are abstracted and further developments are discussed. Finally we conclude that the analysis based on the functional zones, emphasizing the relations between the cities and the mode of combining qualitative analysis with quantitative analysis are the developing trends of the method. Facing to the more emergences of the polycentric urban agglomeration and the network urban agglomeration, the method combining spatial statistical analysis based on GIS with the analysis of the flow data among cities would be a better choice for the delimitation of urban agglomeration region. Keywords- urban agglomeration; spatial scope; delimitation; GIS I. INTRODUCTION The geographical region and its boundary are complementary to each other. The former is the basis for the existence of the latter, and the latter identifies the former. Many scholars have defined the boundary of the geographical region from different perspectives, but their definitions share some degrees of similarities, i.e., geographical boundary is a line or transitional zone of distinction between geographical units as well as the signs of regional diversity for adjacent regions, and it works on the interaction between the regions. Geographical boundary not only functions as the division between the adjacent regions, also serves as a tie of the contact between the regions (Champion and Monnesland, 1996). As a particular geographical unit, urban agglomeration is a spatial unit of urban group based on the demand of integrating the economic and environmental features (Shi and Zhou, 1997; Capello, 2000). There is no established administrative boundary, therefore, the studies on urban agglomeration should firstly delimitate the spatial scope of urban agglomeration. Meanwhile in order to ensure a reasonable integration of the functions among the cities in a certain region, it is important that there is a clear and reasonable spatial scope of urban agglomeration. Obviously it is the foundation of the various studies on urban agglomeration, and it is the basis for the development policies of urban agglomeration emphasized in the China's 11th Five-Year Plan. The delimitation of urban agglomeration region has been a challenging problem for a long time (Hong and Huang, 2007; Eckhardt, 2008). Since the notion of urban agglomeration was introduced, the research on the delimitation for the spatial scope of urban agglomeration was related to the study on the concept of urban agglomeration. Today, the concept of urban agglomeration which was recognized by most scholars is that the urban agglomeration refers to certain integrated aggregation which involves some cities with different characteristics, types, scales in a certain area, and centered with one mega city or two, the internal ties among these different cities reinforces constantly in context of given environmental, traffic conditions and advanced information network (Yao, 2001). Interpreting this concept we can get farther cognition about urban agglomeration (Figure 1), and it will help to understand the methods of delimitation for the spatial scope of urban agglomeration. At present, based on such concept, many theories of regional economics, urban geography, economic geography, and other disciplines combined with GIS, statistical analysis and other technologies have been applied to the delimitation for the spatial scope of urban agglomeration by many scholars. But thinking about the concept of urban agglomeration, we can find out that the spatial boundary of urban agglomeration changes gradually (Wilson, 2000). When we try to ascertain the boundary of the mutative region, we must interpret the fuzzy characteristics of the boundary. Additionally, the data for delimitating the spatial scope of urban agglomeration are lacking, and this fact makes it difficult to adopt the ideal methods. Meanwhile, urban agglomeration is always in the development of a dynamic, evolving process (Shi and Zhou, 1997; Wu, 2002). Obviously the spatial boundary of urban agglomeration is dynamic and fuzzy, which has brought a lot of troubles to the studies on the method of delimitation for the spatial scope of urban agglomeration. But from a different perspective, it means the further study can be developed in this field. Supported by National Natural Science Foundation of China (No ) and the Ph.D. Programs Foundation of Ministry of Education of China (No ).

2 II. STUDY AREA AND DATA A. Cognition and Delimitation of Urban Agglomeration Since the concept of Megalopolis was introduced by Gottman (1957) and Gottman (1961), many studies have been developed in this field by various scholars and governmental Figure 1 Interpreting the concept of urban agglomeration organs. The concept and delimitation of urban agglomeration are always the important issues in these studies, and many achievements have been acquired and applied (Table 1). Viewing the process of the studies on urban agglomeration, we can find out that the cognitive process of urban agglomeration is also the process to delimit urban agglomeration, the delimitation of urban agglomeration region is based on the cognition of urban agglomeration. Table 1 Characteristics of a number of studies on the concept and delimitation of urban agglomeration region Publication(s) Berry et al.(1968); Bourne and Simmons(1978); US Census Bureau(2000, 2005) Issue concept and delimitation of SMSA(Standard Metropolitan Statistical Area), PMSA(Primary Metropolitan Statistical Area), CMSA(Consolidated Metropolitan Statistical Area), MSA(Metropolitan Statistical Area) Geographic Location Lynch(1980) concept and delimitation of dispersed metropolis USA Song(1980); Tatakashi and Wang (1990); Akira(1990); Lin et al.(2003) concept and delimitation of metropolitan area, metropolitan region Japan Mcgee(1989); Ginsburg(1991); Jamieson(1991) concept and delimitation of Desakota Southeast Asia Zhou and Shi(1995); Hu et al.(2000) concept and delimitation of metropolitan interlocking region China Yao (2001) concept and delimitation of urban agglomerations in China China Cheshire and Hay(1989); Combes and Overman(2004) concept and delimitation of urban agglomerations, concept and delimitation of FUR(functional urban regions) in Western Europe Northwest Europe Hall(1971) concept and delimitation of Megalopolis England Table 2 Two types of the methodology for delimitating the urban agglomeration region delimitation based on the functional zones delimitation based on the landscape structure Key words function entity Issue urban functional relationship spatial structure and spatial morphology Approach figure the functional urban area analyze the landscape Key data socio-economic statistical data spatial data Perspective explanatory descriptive Representative Methods key indicators distribution analysis, radiant ability of central city-based analysis, distribution density of the cities, fractal scale, manpower visual interpretation based on remote sensing images modeling analysis, multi-factor overlay analysis, spatial correlation analysis Application early/widely latter/fewer USA

3 With the change of the cognition about urban agglomeration, a variety of methodologies of delimitation of urban agglomeration region has been proposed. According to the different process in delimitating urban agglomeration region, we categorize the methodology of delimitation of urban agglomeration region into two types: delimitation based on the functional zones and delimitation based on the landscape structure (Table 2). Delimitation based on the functional zones focuses on the influence of the cities and analyzes the interaction between the cities and environment. Mainly supported by the socioeconomic statistical data, it constructs the indicator system which can be used to determine the urban function. Then it analyzes the spatial distribution of these data in the region in order to ascertain the geographical homogeneity and heterogeneity of the spatial patterns of these indicators. Finally the result is used to delimitate the spatial scope of urban agglomeration. At present, most of methods follow this methodology, and have been adopted widely. The following sections highlight the representative methods and a number of existing examples. Delimitation based on the landscape structure deals with the spatial data of urban agglomeration regions and tries to get the homogeneity of the landscape based on the analysis of the structure and morphology of urban agglomeration region. It uses the homogeneity of the landscape as the gist of the delimitation, extracts the spatial scope of urban agglomeration and confirms its boundary. Following this methodology, the distribution density of the cities (Dai, 1998; Qiao and Li, 2006), fractal scale (Liu and Chen, 1995; Zhao and Feng, 2003; Ma et al., 2007; Fang et al., 2007), manpower visual interpretation based on remote sensing images (Peng, 2003; He et al., 2005; Zhang et al., 2006) were the representative methods which have been applied to delimitate the spatial scope of urban agglomeration region. III. METHODS TO DELIMITATING URBAN AGGLOMERATION REGION As aforementioned, the delimitation of urban agglomeration region is based on its concept. Thus various methods have been constructed because of the different technical supports and the different aspects emphasized by researchers when focusing on the concept of urban agglomeration. This section reviews methods which have been applied widely so far, categorizes these methods, and discusses the strengths and weaknesses of five broad, partly overlapping categories of methods: key indicators distribution analysis, radiant ability of central city-based analysis, modeling analysis, multi-factor overlay analysis and spatial correlation analysis. A. Key Indicators Distribution Analysis This method divides the delimitation for the spatial scope of urban agglomeration into two parts: the delimitation of the central city and its peripheral hinterland. Urban population or non-rural population or economy scale is regarded as the primary criterion for the delimitation of the central city. Based on the delimitation of the central city, the spatial proximity is considered to delimitate the peripheral hinterland; On the other hand, the proportion of non-rural population, the proportion of non-rural economy, the commuting rate of the central city, population density and other indicators is used as the criterion of judgment. Key indicators distribution analysis is the original method of the delimitation for the spatial scope of urban agglomeration. It is applied widely, and many other methods are derived from this method. Typical applications of this method include the concept and definition of SMSA, PMSA, CSMA and MSA introduced by US Census Bureau as well as the similar studies (Berry et al., 1968; Bourne and Simmons, 1978; US Census Bureau, 2005). At the same time, some scholars from various countries applied this method to delimitating the urban agglomeration or the similar regions based on the local conditions. Morikawa (1985, 2006), Tatakashi (1990) and Akira (1990) developed this method and applied it to the delimitation of Japanese metropolitan area. Mcgee (1989), Ginsburg (1991) and Jamieson (1991) introduced the concept of Desakota based on the local conditions in Southeast Asia and applied this method to delimitate it. Martin (1998) introduced the quantitative calculation to the application of this method, and contributed to the quantitative development of this method. Learned from the overseas studies, Zhou et al. (1995) and Hu et al. (2000) reconstructed and applied successfully this method to the delimitation for the spatial scope of urban agglomeration in China. A variety of successful applications of this method (Sun, 1992; Sun, 1995; Yan, 1997; Hu, 1997; Ning, 1998; Yao, 2001; Gu and Yu, 2002; Jiang, 2004; Gao and Ning, 2007) have supported the regional planning effectively. In general, this method emphasizes the characteristics of regionality and clustering of urban agglomeration. The qualitative analysis is the primary means of this method, and the subjective empirical analysis is combined with the expert knowledge in this method for obtaining the final result. A major drawback of such method is that the result from this method has a certain degree of subjectivity. Because of the practicability and wieldy of this method, it is reconstructed for China s national conditions and applied widely by many Chinese scholars. It is worth noting that when some studies attempted to form a common criterion for delimitating the spatial scope of urban agglomeration based on this method, they ignored the specific conditions of different regions. B. Radiant Ability of Central City-based Analysis This method can also be divided into two parts. One is the delimitation of the central city; the other is the delimitation of the peripheral hinterland. And urban population or non-rural population or economy scale is also regarded as the primary index for the delimitation of the central city. Distinctively, this method focuses on the analysis of the radiant ability of the central city, and identifies the spatial scope which can be

4 influenced to a certain extent by the central city in order to delimitate the spatial scope of the peripheral hinterland. To calculate the radiant ability of the central city, the distance between the surrounding cities and the central city is the major measuring index. In this method it ascertains the potential energy level or the circle domain radius of the central city based on its population or economy scale firstly. Then the distance between the surrounding cities and the central city is calculated, and the scope of the peripheral hinterland is delimitated by judging whether the distance falls within the range of the potential energy of the central city. Obviously, how to calculate the distance between the surrounding cities and the central city is the key of this method. In this field many methods for distance calculating have been developed and applied widely, and it is no longer confined to the traditional calculation of the distance. The weighted distance such as time distance and economic distance is calculated and applied to the delimitation of the peripheral hinterland. Wang and Guo (2003), Feng and Wang (2006) adopted this method to delimitate the spatial scope of urban agglomeration based on the calculation of time distance. In order to delimitate the spatial scope of urban agglomeration, Gao and Luo (1998) and Yang et al. (2007) also adopted this method, but the economic distance was used during the study. This method focuses on the characteristic of the centricity of urban agglomeration. The radiant ability of the central city is emphasized excessively. The reaction and the urban scale of the surrounding cities are ignored. At the same time, the empirical qualitative analysis is still in dominant position in this method, and it leads to the results have a certain degree of subjectivity. But the technical characteristic of such method reflects the mode that combines the qualitative analysis with the quantitative analysis can be used to delimitate the spatial scope of urban agglomeration more accurately. C. Modeling Analysis Modeling analysis is the most important field of the research on the theory, method and application of geocomputation which was introduced and developed rapidly in the 1990s (Richard, 1997). It has been applied widely in many fields of the geographic research including the delimitation for the spatial scope of urban agglomeration. At present, from the perspective of the study on interaction among the cities, this method is based mainly on the theory of spatial reaction and the distance attenuation principle, and applied the models such as gravity model, field model and so on to delimitate the spatial scope of urban agglomeration. It can be found out after further analysis that this method relies on some of the mature theoretical models firstly. Generally, the laws and phenomena that these models reflected are able to find a similar scene in the fields of the study on urban agglomeration, such as the scene of the interaction between objects described by the gravity model is very similar to the interaction between the cities within urban agglomeration. Secondly, the model is rebuilt through the reasonable replacement of the parameters of the original model, and the parameters of the original model are substituted by the main factors of the existing research, such as Equation 1 and Equation 2 are the reconstruction of gravity model and field model respectively. Y PG PG = (1) i i c c ic 2 Eic C PG = (2) c c ic 2 Eic where Y is the value of the gravity between the cities, C is the value of the field intensity of the central city, P is the number of the urban population in the urban areas, G is the value of the GDP of urban area, E is the distance between the surrounding cities and the central city, i is the surrounding city and c is the central city (Jiang, 2004; Li and Ji, 2007). Finally the new model can be used to simulate the interaction between the cities, analyze the relationship between the cities quantitatively, and the spatial scope of urban agglomeration can be delimitated based on the result of foregoing analysis. Modeling analysis has underlain many studies on the delimitation for the spatial scope of urban agglomeration. Tan and Yang (2000) applied gravity model and field model to the delimitation of urban agglomeration, and selected urban population in the urban areas, GDP of urban area, time distance between the cities, accessibility factor of politics and culture, and correction factor of acceptance as the characteristic indices for the delimitation. Jiang (2004), Miao and Wang (2006), Li and Ji (2007) also used the gravity model and field model to construct the judgment vector for the delimitation of urban agglomeration. This method is mainly based on and considers adequately the characteristic of the interaction between the cities, which is one of the important characteristics of urban agglomeration and influences markedly the composition and the spatial scope of urban agglomeration. However, the actual modeling analysis usually applies mechanically the mature model and formula, and the parameters of the model are limited in the few aspects, such as population and economic. It can not take more factors into the analysis and carry out the study from different views. Finally it is worth noting that a major significance of such method is that it has established the foundation for the study on the universal method of delimitation for the spatial scope of urban agglomeration. D. Multi-factor Overlay Analysis This method regards the delimitation for the spatial scope of urban agglomeration as the process of spatial overlay analysis. A number of factors which influence the spatial scope of urban agglomeration are analyzed respectively, and the results are used to spatial overlay analysis. The steps of this method can be described as follows: First of all, the dominant factors are generalized through the qualitative analysis based on local conditions. In the second part, it usually has two different analysis means. One is the spatial overlay analysis based on GIS. That is, each dominant factor

5 is analyzed firstly, then, the spatial scope of urban agglomeration is delimitated based on spatial overlay analysis using the results of dominant factors analysis based on GIS. Sun (2003), Cheng et al. (2003), Wang et al. (2007) summed up the dominant factors which influence the spatial scope of urban agglomeration including the space, time, flow and gravity. Each of these factors was regarded as a criterion of the delimitation respectively, and the different scope of urban agglomeration was obtained. The final scope of urban agglomeration was estimated through the spatial overlay analysis based on GIS using these results. At the same time the intersection, union, complement set of these results was computed using GIS respectively in their studies, and the scope of the corresponding circle area of urban agglomeration was analyzed. Qiao and Li (2006) used the theory of density analysis as well as the contrastive idea to study the gather degree of the cities and towns within a certain region. Three issues were carried out in this study including the development degree of city node (cities at all levels), the relation intensity of transportation networks and the development level of substrates. They also used the means of spatial overlay analysis based on GIS and the analytic conclusion of all issues to analyze the scope and structure of urban agglomeration. The other is to construct the multi-factor judgment vector. That is, the threshold of each dominant factor which reflects the minimum criterion of each dominant factor for judging whether a city belongs to urban agglomeration is calculated and used to make up of the multi-factor judgment vector. The values of the dominant factors shown by all cities within a certain region will be compared with the multi-factor judgment vector for testing whether the city meets the conditions of urban agglomeration. Finally, all cities which should belong to urban agglomeration are ascertained, and this result is used to delimitate the composition and scope of urban agglomeration. Li and Ji (2007) constructed the multi-factor judgment vector composed of economic distance, the value of gravity and the intensity of field. Whereafter, the multi-factor judgment vector was used to estimate the composition and spatial scope of urban agglomeration in their study. The major superiority of this method is that it takes more factors to the delimitation for the spatial scope of urban agglomeration. It improves the accuracy of the result and makes the result closer to the objective reality. However, the factors which are interdependent and interrelated in nature are separated severely for the analysis in this method. Although the analytic result of each factor is used to perform spatial overlay analysis, and the final result is based on the analysis of spatial overlay. But obviously it ignores the interaction between the factors, and this will lead to the difference between the final result and the actuality. Interpreting this method from the perspective of technical characteristics, it also reflects the mode that combines the qualitative analysis with the quantitative analysis and the application of the quantitative analysis based on GIS. E. Spatial Correlation Analysis This method is established in the cognition of the concept about urban agglomeration is an organic aggregation composed of a number of cities. It mostly delimitates the spatial scope of urban agglomeration based on the analysis of the relationships between the cities within the region, and can be roughly divided into two categories (Figure 2): one is to delimitate the spatial scope of urban agglomeration through measuring the relationships between the cities, especially the relationships between the central city and the surrounding cities. The threshold to determine whether the cities belong to the urban agglomeration will be calculated and defined according to the analysis of the relation intensity between the cities in the aspects of traffic, economy, and society and so on. Finally the threshold will be used to determine whether a city belongs to the urban agglomeration and delimitate the spatial scope of urban agglomeration; the other is the application of the statistical analysis in the measuring the relationships between the cities. It classifies the cities through the statistical analysis based on a large number of sample data, and the classification result is regarded as the key indicator for delimitating the spatial scope of urban agglomeration. Considering the application of the different kind of the statistical analysis in this method, it can be further divided into two categories: application of the general mathematical statistic analysis and application of the spatial statistical analysis. Yu and Wu (2005), Yu (2006) used the integrated administrative region as the geographic units for analyzing, and regarded each unit as a homogeneous region. They applied the mathematical statistic analysis such as principal component analysis and clustering analysis to classify these geographic units and delimitate the spatial scope of urban agglomeration. The statistical data of each geographic unit about the economy, society and so on were the sample data for the analysis. This can be regarded as one of the representative studies of the former. The latter is a new method emerging recently for the delimitation of urban agglomeration. It pays attention to the cities characteristic of spatial autocorrelation within the region because of the impact of the continuity in the geographical distribution. And it usually applies the means of spatial quantization based on the spatial statistical characteristic of the indicators and GIS data model to analyze the relevant indicators and data in order to establish the relationship between the spatial unit and its attribute (Ye et al., 2005; Fang et al., 2005). The cities are viewed as the points or the regions distributing in the space, and analyzed as the spatial variables in order to get the spatial distribution characteristics. Finally these characteristics are used to delimitate the scope of urban agglomeration supported by the analysis such as the breaking point analysis, the analysis based on Voronoi diagram and so on. This method focuses on the characteristic of the spatial correlation of urban agglomeration. The interactions along with the relationship between the cities within the region are still the start of the study. Interpreting all forms of this method, the delimitation through measuring the relationships between the central city and the surrounding cities has a major

6 drawback that only the partial indicators can be considered in such method. Obviously, it will affect the accuracy of the result. The delimitation based on the general mathematical statistic analysis only focus on the socio-economic statistical data and ignores the spatial characteristics of the cities. Meanwhile, the administrative regions are the basic geographical unit for the analysis. The indicators and statistical data are used based on the administrative regions strictly. This simple statistical description only reflects the cities spatial characteristics in administration and does not accord with the actual distribution of the physical urban area. It would lead to biases between the final result and the reality. Considering the aforementioned problems, the spatial variable is introduced to the delimitation based on the spatial statistic analysis. Geographical entity itself is linked to the geographical location of the entity for analysis, and GIS spatial data model along with GIS spatial analysis methods are drew on in this method. The spatial characteristic of the city is combined with its other attributes for analysis. At the same time, the applications of the quantitative analysis based on GIS and the analysis based on breaking the administrative districts in this method show us a good idea for improving the accuracy and enhancing the universality of the method. Figure 2 Classification of the method of delimitating the spatial scope of urban agglomeration based on spatial correlation analysis IV. IDENTIFICATION OF THE COMMON CHARACTERISTICS EXISTING IN THE CURRENT METHODS A. Most of the Existing Methods are More Concerned on the Concept of Urban Agglomeration in an Economic Context. The Concept of Urban Agglomeration was Given to the Connotation of Economics, and a Certain Geographical Region was usually Regarded as an Economic Region. In the current background of complex socio-economics, urban agglomeration is not only a concept in geography. More importantly, it contains the meaning of economics (Scott, 2001; He et al., 2004; Eckhardt, 2008). In particular, the rapid developments of modern transportation mode and communication technology have reduced the transportation costs and time costs. The direction, speed and frequency of material and non-material flow between the cities as well as between the cities and the region have been changed, and the spatial operation mode of economic activity also has been changed fundamentally. Simultaneously, the radiant ability of the cities has been enhanced so that the interactions between the cities as well as between the cities and the regions are further strengthened, and the social economic linkages become closer. Evidently, the urban agglomeration has been a special kind of spatial organization for the development of regional economy. Therefore, many scholars fully draw on the economic characteristics of urban agglomeration when they delimitate the spatial scope of urban agglomeration, and the economic scale, the economic linkages between the cities as well as between the cities and the region are regarded as the key indicators. B. Most of the Existing Methods either Clearly or Vaguely Followed the Course Which can be Described that the Central City was Defined firstly, and then the Spatial Scope of the Peripheral Hinterland was Delimitated. In the concept of urban agglomeration, there is two points, that is "centered with one mega city or two" and" certain integrated aggregation which involves some cities with different characteristics, types, scales in a certain area" (Yao, 2001). Therefore, the existing methods usually considered the functional relations between the surrounding cities and the central city subjectively as well as the integration of the entire area, and followed the above course for delimitation by and large. During the process of defining the central city, population scale, economic scale, urban synthetic scale, intensity of urban flow, and other indicators as well as the compound indicators composed of several before-mentioned indicators are usually regarded as the key indicators. The delimitation of the peripheral hinterland s scope is based on the achievement of the definition of the central city, and the diversity of many methods for delimitating the spatial scope of urban agglomeration is reflected basically in the means of delimitating the peripheral hinterland. In general, the analysis

7 of the relationship between the surrounding cities and the central city is used to delimitate the peripheral hinterland. C. The Methods Based on the Analysis of Functional Area are Prevailing. Urban areas may be conceived as administrative, functional and physical entities. Administrative urban area is clearly delimitated with the establishment of urban; physical urban area is delimitated based on attempting to accurately reflect the geographical landscape scale of urban; functional urban area is the area which can reflect the basal functions of urban including the habitation, employment, shopping, medical treatment, recreation and so on, and it makes up of the city s core and the surrounding area which keeps close relationship with the city s core (Batty and Longley, 1994; Karlsson et al.,2006). To delimitating the spatial scope of urban agglomeration, these three categories for the concept of the urban areas also can be used. At present, despite the administrative area of urban agglomeration in China is not as clear as its application in the city, but in many regions the union established by a number of cities for the development of the regional economy usually defines the composition and scope of urban agglomeration by taking the urban area as the basic unit, such as the Forum for the Coordination of Urban Economy of Yangtze River Delta Region plays an important role in the delimitation of the urban agglomeration of the Yangtze River Delta. The concept of physical area and functional area can be used as their applications in the city, and most of existing methods for the delimitation of the scope of urban agglomeration are usually based on the analysis of functional area, that is, the scope of urban agglomeration is delimitated from the perspective of the functional relationship between the cities. This is inseparable from the prevalent cognition that urban agglomeration is a functional urban area. V. CHALLENGES AND DEVELOPMENT Many methods have been explored and applied by researchers when delimitating the spatial scope of urban agglomeration. Perceptibly, with the further learning about urban agglomeration as well as the development of the relevant technology, the method for delimitating the spatial scope of urban agglomeration must obtain greater development based on the existing methods. At the same time, there remain a number of fundamental challenges for which no clear solutions exist, such as how to improve the accuracy of the results and the universality of the method as well as the consideration of the unique characteristics of urbanization in China and so on. These issues must be addressed in the coming years in order for the delimitation of the scope of urban agglomeration to evolve into a mature scientific field. A. The Diversity of the Factors Which Affect the Development of Urban Agglomeration should be Paid Attention to much more, and the Research Perspective in the Method of Delimitation for the Spatial Scope of Urban Agglomeration should be Increased. Urban agglomeration is a product of the interaction between the city and the region. The factors which affect the interaction are multiplex (Guo et al., 2007). The close economic relationships among the cities are only a prerequisite of constructing urban agglomeration, not a necessary condition. Many factors such as the administrative subjection relation, cultural identity, industrial structure, population, topography and other factors should also be considered synthetically during the process of delimitating the scope of urban agglomeration. So the method of delimitation for the spatial scope of urban agglomeration should be studied and developed from more perspectives, and the method based on integrating multi-factor analysis should be developed. B. The Method for Delimitating the Spatial Scope of Urban Agglomeration which is According with the Characteristics of Urbanization in China should be Explored. The process and the status quo of urbanization in China are different from other countries, especially the developed countries in the West. In fact, many methods for delimitating the spatial scope of urban agglomeration which have applied successfully in the developed countries in the West do not fit in with the urban agglomeration in China. For example, the commuting rate emphasized by the methods applied in the developed countries is not the main way of reflecting the contact between the urban and rural in China. At present, the suburbanization in China is limited to the suburbanization of the population; the suburbanization of the industry has not yet formed a certain scale; the suburbanization of the retailing and the office also needs for a period of time, and urban road networks as well as private cars are far from being fully developed (Qiao and Li, 2006). As a result, according to the unique status quo of urbanization in China, it is very necessary to explore the methods for delimitating the spatial scope of urban agglomeration which according with the characteristics of urbanization in China. C. The Quantitative Analysis and the Quantitative Model should be Strengthened. The method for delimitating the spatial scope of urban agglomeration is also undergoing a process from the qualitative analysis to the quantitative analysis. Admittedly, the qualitative description based on the quantitative analysis will redound to improve the accuracy of the delimitation. However, the current methods for delimitating the spatial scope of urban agglomeration are also mainly based on the qualitative analysis, and the quantitative analysis is only applied to the partial indicators. The further study on the quantitative analysis and the quantitative model which can be used to delimitate the spatial scope of urban agglomeration should be carried out. The quantitative analysis of indicators

8 based on GIS, the quantitative statistical analysis and the quantitative analysis of other disciplines should be introduced into the method for delimitating the spatial scope of urban agglomeration, and it will greatly enhance the effectiveness of the qualitative description as well as the accuracy of the delimitation. D. Emphasizing the Network Developing Trends of Urban Agglomeration, the Method for Delimitating the Spatial Scope of Urban Agglomeration which Adapts to be Used in the Network Urban Agglomeration and the Polycentric Urban Agglomeration should be Explored. In general, the spatial structure of urban agglomeration includes one mega city or two as the central cities and the neighboring areas which have a high degree of socioeconomic relation with the central cities. However, with the rapid development of information technology and the construction of modern rapid transit system, the trend of urban decentralization is increasingly clear. It has led to the change of the spatial structure of urban agglomeration from the traditional monocentric structure to the network or the polycentric structure (Capello, 2000; Rafael and Joan, 2007; Gu et al., 2007). The spatial structure of urban agglomeration tends to become complicated. Cities within urban agglomeration form a flat network regional space through the organic relation in the function and space in order to meet the needs of the information society (Scott, 2001; Yao, 2001; Morikawa, 2006). For example, the formation of Changsha- Zhuzhou-Xiangtan urban agglomeration and Suzhou-Wuxi- Changzhou urban agglomeration in China is adapted to the trend of the spatial evolution of urban agglomeration in the information age. They are not derived from the traditional urban space sprawl, but the unique and flexible network urban agglomeration which are polycentric constructed by a number of different city nodes. Accordingly, facing the developing trends of spatial structure of urban agglomeration, the method for delimitating the spatial scope of urban agglomeration which adapts to be used in the network urban agglomeration and the polycentric urban agglomeration should be explored. E. Strengthening the Introduction of the Spatial Information Technology in the Method of Delimitation for the Spatial Scope of Urban Agglomeration, the Analysis of the Spatial Characteristics should be Combined with the Analysis of other attributes Characteristics in Order to Enhance the Spatiality of the Result and more Objectively Reflect the Spatial Scope of Urban Agglomeration. The traditional methods take the administrative units as the basic unit of the delimitation, and analyze the spatial structure as well as the spatial scope of urban agglomeration through the mode of non-spatial characteristics. As a result, the analysis result lacks the spatiality so that it has impacted its application for implementing the planning in the planning administration. Instead of the traditional methods which ignore the spatial characteristics of the cities within the region, the methods which combine the analysis of the spatial interaction, spatial distribution with the analysis of the attributes characteristics based on GIS can delimitate the spatial scope of the urban agglomeration more objectively. And such methods grasp the regional law on the development and evolution of urban agglomeration so as to provide the decision support for urban and regional planning administration. VI. CONCLUSIONS To scientifically standardize and delimitate the spatial scope of urban agglomeration have become an inevitable basic problem. How to delimitate the spatial scope of urban agglomeration, the methods which have different technical characteristics have been explored because of the different cognition about the concept of urban agglomeration by different scholars and the different purposes of the application. However, from the perspective of improving the accuracy and universality of the method for delimitating the spatial scope of urban agglomeration, the analysis based on the functional zones, emphasizing the relation between the cities and the mode of combining qualitative analysis with quantitative analysis will be the developing trends. At the same time, with the development of urbanization in the world, the concept of urban agglomeration has been updated and expanded gradually. Thus the method of delimitation for the spatial scope of urban agglomeration rooted in the concept of urban agglomeration should also be refined constantly in order to adapt to the development of urban agglomeration. It is worth noting that the intensity and the way of the interactions implemented by various flows between the cities and the region as well as between the cities have been changed constantly following the development of modern communications technology and transportation. The spatial structure of urban agglomeration is evolving from the discrete structure to the Pole Axis structure and from the single-core structure to the network structure. The concept of urban agglomeration which takes one mega city or two as the regional economic core has no longer possessed universal significance. The emergences of the network urban agglomeration as well as the polycentric urban agglomeration are a major change following the development of urban agglomeration. Accordingly, the traditional methods adapted to delimitate the spatial scope of monocentric urban agglomeration will dissatisfy with the development of urban agglomeration, and they will have an obvious drawback in the aspect of universality. Therefore, in order to adapt to the emergences of the polycentric urban agglomeration as well as the network developing trends of urban agglomeration, together with the developing trends of the method, the method combines spatial statistical analysis based on GIS with the analysis of the flow data between the cities is expected to become a promising choice for the delimitation of urban agglomeration region. [1] American Census Bureau, Standards for Defining Metropolitan and Micropolitan Statistical Areas. Federal Register Notices, , 2000.

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