| The Tibetan Plateau is a plateau region with the most distinctive features of the natural and human environment on the earth.It is known as the “third pole of the world”.Its ecological environment is extremely sensitive and fragile.The natural environment in which human beings live is highly constrained,and the resources and environmental carrying capacity are weak,the production and lifestyle are unique,the social and economic development is lagging,the level of urbanization is low and the radiation-driven ability is weak.The special geographical environment and development background determine the uniqueness of its settlement characteristics;however,due to the lack of basic data and difficulty in obtaining,it is difficult to enter,the settlement size is generally small and the distribution is scattered.In the past,data based on land type or computer remote sensing interpretation is difficult to effectively describe the form of settlement,which makes the existing research rarely involved in this area,and it cannot provide effective decision support for the settlement development in the Tibetan Plateau.Therefore,the search for effective research methods for the settlement of such areas is an important research topic for both the development of the discipline and the actual needs.Taking Nagqu County in the northern Tibetan Plateau Pastoral Area as the research object,following "cognition-evaluation-construction",the basic path for human beings to adapt and transform their living environment,adopting the classical geography research paradigm of “pattern-mechanism-regulation” as the overall analysis path,based on settlements spatial data which is accurately extracted from multi-temporal high-resolution remote sensing images during 2005-2017,through the comprehensive application of GIS analysis technology,this paper quantitatively measures the overall characteristics and spatial orientation characteristics of the settlement evolution in Nagqu County,and further explores the driving mechanism of settlement pattern and evolution.In addition,constructing the evaluation index system of settlement land suitability including natural geography,ecological environment,social economy,this paper divides the suitability type of settlement land using the SOFM neural network and evaluates the suitability of current settlement land,and on this basis,further explores the path of settlement reconstruction.Main conclusions are as follows:(1)During 2005-2017,the evolution of settlements in Nagqu County showed a phased feature.The concentrated settlement during the “Eleventh Five-Year Plan” period led to the expansion of the number of settlement patches.During the "Twelfth Five-Year Plan" and beyond,infrastructure construction and the diversified development of settlement functions promoted the increase of settlement scale.The settlements expansion intensity is limited,Nagqu Town is unique.The evolution of settlements pattern shows a staged difference,from spatial disorder to regular order.The settlements of Nagqu County is mainly small,and the proportion of plaques with an area of less than 1 hm2 is as high as 69%.As time evolves,small settlements gradually transform into large and medium-sized settlements.The overall pattern of settlements shows a stable agglomeration situation.The large-scale plaque agglomeration area is centered on the location of the county seat and extends southwest along the Qinghai-Tibet Highway.The small-scale plaque agglomeration area has a “circular” distribution around the periphery of Nagqu Town.(2)The special natural background has shaped the low altitude and gentle slope trend and hydrophilic near-road characteristics of settlements in Nagqu County.Affected by the living environment and livelihood methods,settlements are often distributed in areas with low natural disasters,and the settlement evolution shows high-quality grassland pointing.And with the increasingly strengthening of the economic functions of the plateau towns,the evolution of settlements in Nagqu County gradually shows the center of the township which is similar to urbanized areas of the interior.High-altitude,broken landforms,frequent occurrence of natural disasters,differences in pasture endowments,and vertical and horizontal water system have shaped the basic settlements pattern of scattered distribution of large-scale small-scale terraces along the river valley in Nagqu County.Social and human factors such as policy,marketization and population growth,location conditions,management systems and cultural concepts are the main driving forces for the evolution of settlements in Nagqu County.(3)The suitability level of settlement land in Nagqu County is generally low,appropriate areas and suitable areas only account for 12% of the total area of the county distributing in the mountain valleys where is low altitude and flat,the degree of suitability is lower than and equal to the generally suitable areas concentrate contiguous distribution,accounting for 88%.There is a significant difference in the suitability level of settlement land in every township.The proportion of settlements in the areas that the degree of suitability is higher than and equal to the generally suitable is 86.47%,and 13.33% of the settlement area still distributes in less suitable,inappropriate and prohibited areas.Settlements distribution of various townships tends to high-grade suitability areas,the layout of settlements in townships with good natural and environmental conditions is reasonable and vice versa.Missing planning guidelines,unreasonable administrative division,local identity to the specific living space and the Tibetan Religious worship of mountains all lead to the unreasonable layout of the settlement in Nagqu County.(4)Through ecological immigration and promoting moderate concentration of settlements in suitable areas to adjust factors of settlements to realize spatial reconstruction of settlements.Push reorganization of settlements structure by promoting the construction of central villages and towns and exploiting the diffusion of elements from the “point-axis” network to realize economic restructuring of settlements.Optimize function of settlements by improving public service facility configuration and promoting the degree of social organization and inheriting Tibetan culture to realize social restructuring of settlements. |
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