2. Methodology
2.1. Definition and concept
The definition of urban agglomeration hasn’t been in a robust consensus both at home and abroad.
The foreign terms related to urban agglomeration are as follows, Megalopolis [5], Town Cluster [6],
Courbation, Urban Agglomeration[7], Metropolitan Area[8], Desakota[9] and so on. While in China,
the corresponding terms are as follows, Urban Concentrated Region, City-and-Town Concentration
Area [10], Metropolitan Area, Metropolitan Interlocking Region [11], Metropolis [12] and so on.
After comprehensive consideration of various expressions and analyses of relevant concepts, this
paper deems that the most common and essential characteristics of urban agglomeration lie in three
aspects, that is, the centralization of national elements, the decentralization of regional elements and
the connection between cities. Besides, it’s noteworthy that metropolitan area is the basic and
indispensable component unit of urban agglomeration. Accordingly, this paper is oriented towards
the evolution of urban agglomeration, which ranges from built-up area, municipal district,
metropolitan area, joint metropolitan area (or metropolis) to metropolitan interlocking region. To be
more specific, the built-up area is physically built area within a certain city, the municipal district is a
kind of urban region under the administrative jurisdiction of a single government, the metropolitan
area is the basic functionally component unit of urban agglomeration, which links the urban and rural
closely together, and finally the joint metropolitan area and metropolitan interlocking region are the
primary forms of urban agglomeration. From the perspective of spatial scale, metropolitan area is
generally the extended linkage area of urban and rural 50 km away from the built area. Moreover, the
joint metropolitan area covers an area with a radiation radius of 100 km and the quasi metropolitan
interlocking region covers an area closely linked with a radiation radius of 200 km. The most
advanced form, metropolitan interlocking region covers an extended area with a radiation radius of
300 km. In the wake of economic development to a certain extent, the centralization of
non-agriculture industry and other urban functions commences exerting an ever-growing impact on
the surrounding areas, leading to high social and economic ties between the central city and the
surrounding areas to a certain range. On the basis of tied connections, a new form bearing the
intention of integration called Functional Urban Regions [13] thus comes into being with sharing of
resources, environment and infrastructure as well as close relevancy of industrial economic activities.
Functional urban regions are composed of the core city and its surrounding areas which maintain
close relationship with the core city, providing basic functions like residence, employment, shopping,
medical care and recreational activities [14]. Joint metropolitan area is highly connected intercity
area which is made up of several coterminous metropolitan areas with tied social and economic
connections. Following this logic, joint metropolitan area is the component unit of metropolitan
interlocking region. Metropolitan interlocking region is a giant urban and rural integration area cored
on several big cities, develops along transportation corridors and maintains strong interaction in
social and economic ties with surrounding areas [15]. For one thing, metropolitan interlocking region
itself is the result of spatial concentration of various physical and non-physical elements. For another,
metropolitan interlocking region is also the phenomenon presented in the stage of gradually
dispersed development instead of absolute concentration during the process of urbanization.
Concentration goes hand in hand with the function of hub and incubator, while the dispersion is the
reasonable logical extension of incubator. Thus, the dual processes of concentration and dispersion
strengthen the regional poly-centric structure and render continuous impetus for the metropolitan area.
Exactly in such a continuous and dynamic process under the dual interaction power of concentration
and dispersion in the urban region as the core of social life, the function of hub and incubator
mutually promotes each other and develops unceasingly, thus forming the metropolitan interlocking
region.
The Identification of Developmental Pattern of Urban Agglomerations in China based on GIS
665