On The Urban Development And Urban Spatial Structure Of Valley Cities In The Western China

Urban sustainable development and urban spatial structure evolvement have been a hot spot of urban geographic studies since last century. Chinese academia has made great progress in the fields, but there is limited progress of theoretic general review of the development and spatial structure evolvement of certain cities under special environment and condition. In this article, the development and spatial structure problems of valley-basin cities, which lie in the valley-basin and under the special development environment in Western China are investigated. The purpose is to discuss the probable effect and function of outer factors in different sorts and different intensity to the western valley-basin cities which are under special and complicated natural and human environment in different periods, and find how such kind of cities started and developed, how urban spatial structure evolves and how to solve the problems in the future, such as environmental problem, communication problem and urban landuse problem.In the article, valley-basin city is defined as the cities whose main part (that is the built-up area or the core of the city) formed and developed in the valley-basin. Furthermore, the main part's development is limited intensively by the valley-basin terrain and the mountain or downs around. When urban development reaches certain period, the city itself has to develop along the trend of a river or along the upper part of a mountain's of both sides. According to whether the main part developed along the upper part of a mountain, such kind of cities can be classified into two types, "mountain city" and "valley city". "Valley city" is the city whose main part developed inside the valley, such as Lanzhou. "Mountain city" is the city whose main part developed not only in the valley but also along the upper part of the mountain. It can form peculiar "mountain city landscape", such as Chongqing.Valley-basin cities in the west of China are affected and restricted comprehensively by all sorts of factors, such as natural, social, economical, cultural condition and communication condition. The type, mode and intensity coupled by all sorts of factors are the key link of such kind of cities' development. Only those valley-basin cities, which have good regional social and economic bases, important strategy status and superior location conditions can get strong support from national development plan and fulfill striding development. Their coupled effect of all sorts of factors is the best.Human civilization and human settlement had generated in many valleys long before, because valleys have such natural predominance as terrain, soil, vegetation, water resource and communication. Due to political and military reasons, especially the conflict and amalgamation among different civilization in China, a lot of valley-basin cities started and founded in the west. However, it was the prosperity and aggregation of commerce and handicraft that facilitated the development of valley-basin cities. In the ancient times, the main functions of western valley-basin cities were politic and military, while the roles of commerce, handicraft, communication and culture were in weak status. Only few cities had larger scale, such as Chongqing. Many other cities was of small scale. Western valley-basin cities were distributed widely and had the trend to propel from the Middle of Shaanxi and Sichuan to the outer. As awhole, their distribution was dispersive.In the ancient times, western valley-basin cities' basic material composed factors were divided into four categories, that were, political and military factor, cultural factor, social and economical factor and infrastructure factor. Their spatial structure mostly was built by Han nation and was deeply affected by the culture of Central China. Only a few valley-basin cities truly embodied national culture character. According to the effect degree of terrain to urban spatial distribution, layout and outer morphological character, western valley-basin cities in the ancient times can be divided into standard valley-basin cities and nonstandard valley-basin ones. The common characters of these two kinds of cities are listed as following: cities lied in the place easy to develop agriculture and defense; cities governed the agriculture regions around; cities obtained food from the peasants inside and outside; formed the dual framework in which so-called political urban district (cheng) and economical urban district (xiang) coexisted, and so on. Their different characters include: standard valley-basin cities have well-conformed and well-developed urban outer form; the character of urban integral layout is serious, ordered and with notable spatial solid; normally most of standard valley-basin cities are planned and built by Han nation; nonstandard valley-basin cities can be divided into two types, one embodies Han culture and the other embodies the culture of nations minority; the spatial structure character of nonstandard valley-basin cities that are affected by Han culture has the urban outer form adapted to local conditions, and such kind of cities have been rudimentarily planned and designed; nonstandard valley-basin cities that embody nations minority culture have the track of religion government, relative regular and well-developed urban outer form, square in the city's center, religious building and government construction around.Since the Opium War the west of China has been affected not only by the West World and Russia but also by the east of China. Commercial harbor open-up and the development of communication and industry facilitated the further development of western valley-basin cities. Under the special development environment and the support of government, the movement of modern industry and business, financial capital, population and education from coastland to the inland facilitated valley-basin cities' development. For example, the city of Chongqing was the largest city in the west at the time of the War Resistance Against Japan.But with the movement of industry and business (that once were moved to the inland) to the east, western valley-basin cities' development reduced considerably. As a whole, in this period western valley-basin cities' scale was still small, their function were single and their distribution was wide and dispersive.In the period between the Opium War and the establishment of PRC, western valley-basin cities were affected by the west world,Chinese traditional, feudal force, new regional warlord force and national capital. According their affection degree, valley-basin cities can be divided into the type called notable change and the type called weak impulsion. The spatial structure of the former type's the similar character as the eastern cities that have "abutting" spatial structure, but it is not the main structure. Urban function district is composed of old urban area, business or leasehold area, self-formed industrial area, mixed housing area and planned new urban area. Most of western valley-basin cities belong to the type of weak facilitation. Such kind of cities' spatial structure is affected and impelled by the colonial force and eastern industry and business, but the external force is quite weak and internal force is not strong enough. Therefore, as a whole, their change is limited. Their main characters are listed as following: cities develop and layout around their old center; urban function district is composed of old urban area and expanding new urban area; cities maintain their original relatively regular outer form; urban population density rises alittle and so on.In the modern times, western valley-basin cities got rapid development under the national support. The amount of instituted cities increased greatly. Population, built-up area and economy developed quickly. Spatial distribution of such kind of cities became wider and more dispersive. In particular, with the exploitation of mineral resources in a large scale, a number of resource-exploitation valley-basin cities began to develop. The function of cities changed to comprehensive industrial cities firstly and to comprehensive cities secondly. In the same times, western valley-basin cities' spatial structure is experiencing the most poignant period. Urban internal spatial structure and external form change greatly. The spatial structure of such kind of cities includes the form of conglomeration, parcel, one city and many towns, double cities, big city with satellite cities and so on. It embodies spatial structure's diversity. Urban tract is expanding gradually along valley-basin terrain, distributing discontinuously along valley-basin and mountain, so the larger urban scale, the more apparent the discontinuity of tract layer structure, and the more apparent the mode of multi-center group structure. Because of the affection of valley terrain, river and other natural condition to urban basic function layout and communication network structure, and because of the combination relation of different class tract structure, valley-basin cities' tract structure still obeys the theoretical model of hexagon, although the class system is intact and has some scarcity in tract distribution.Western valley-basin cities' spatial expanding process can be divided into centralized block development period and regional alienating process, professional spillover and dispersive diversified development stage, filling, corresponding and multi-core stage, rural urbanization and urban zoster development stage. Spatial expanding process of different type and different scale cities has some difference, but multi-center group structure is the trend and direction of such kind of cities' spatial structure.Western valley-basin spatial structure evolvement is affected by many factors, such as natural environment, historical development base, urban roles, scale and function structure, transportation mode and accessibility, national policy and planning control, land management mechanism, social and cultural factors, economical development level and economical rules, etc. Social productivity is the fundamental power to the evolvement of urban spatial structure. It can facilitate all factors that affect urban spatial structure's evolvement to change and move in different social and economical environment. The evolvement power of western valley-basin was in a mode combined by natural evolvement and passive evolvement in the passted time. In the present, the main impulsive power is the industrialization process and dispersive layout idea under national support.Because valley terrain restricts the capacity and scale of such kind of cities greatly, urban problems exist earlier in western valley-basin cities that experienced long time development than in other cities. Moreover, these problems normally are severe, such as environment, landscape, land shortage and communication, etc. They are all the key problems of urban sustainable development and should attract more attention.