关键词: 城镇化, 城镇体系, 空间分析, 核密度估计, 城镇重心, 时空演变, 青藏高原

Abstract:

The formation and development of the urban system play a vital role in regional urbanization process and socio-economic development. They also have a significant impact on the eco-environment. Due to the special geographical environment and relatively poor socio-economic foundation, the urban system of the Tibetan Plateau seems less developed. Moreover, the relevant literature in Chinese and English are both scarce, hindering the construction of national ecological security barriers and the sustainable development of the Tibetan Plateau. Therefore, based on statistical data, remote sensing data, and GIS spatial analysis methods, this paper took city proper and urban districts (i.e., the core urban areas of cities and officially established towns in China) as the research object, and analyzed the spatiotemporal evolution patterns of the spatial structure and scale structure of the urban system in the Tibetan Plateau during 1990-2015. Meanwhile, based on the urban gravity center movement model, the spatial patterns of the gravity centers of the urban population and urban construction land in the Tibetan Plateau during 1990-2015 were analyzed. We have four major findings. Firstly, the urban spatial distribution of the Tibetan Plateau shows an overall pattern of "intensive in the southeast, sparse in the northwest" and "globally dispersed, locally agglomerated." Secondly, the number of officially established towns increased with different speeds in three stages. The distribution of the urban system as a whole has been more and more agglomerated and the level of spatial imbalance has been on the rise. However, the upward trend has slowed down markedly since 2005. Thirdly, though the number of officially established towns has increased significantly, the urban populations in 96.88% of them are under 50 000. Large, medium, and small cities are underdeveloped. Fourthly, the gravity centers of the urban population and urban construction land during 1990-2015 were all located in the southeast region of the Tibetan Plateau. The gravity centers of the urban population during 1990-2015 shows a movement direction of "first to the southwest, then to the northeast and southwest." It has moved 116.6 km to the southwest during the entire period. The gravity centers of the urban construction land during 1990-2015 shows the movement direction of "first to the southeast, then to the northwest and northeast." It has moved 43.5 km to the northeast during the entire period. Our findings provide basic data to studies of the new type urbanization and the optimization of urban spatial pattern in the Tibetan Plateau. This paper also provides a method for urban scale estimation under the conditions of data deficiency and statistical caliber inconsistency, which will help advance China's urbanization studies.

Key words: urbanization, urban system, spatial analysis, kernel density estimation, urban gravity center, spatiotemporal evolution, Tibetan Plateau