关键词: 城市用地功能, POI数据, RS解译, 功能变化特征, 长沙市建成区

Abstract: In the context of rapid urbanization, the analysis of urban land use is essential to understand the spatial structure of cities and guide the layout of internal urban spaces. However, rapid and effective methods for identifying the spatial characteristics and dynamic changes in land use functions are unavailable. This study provides a rapid and innovative method to analyze the effects of altered urban land use on spatiotemporal evolution. The changes in urban land function in built-up areas of Changsha in 2012 and 2002 were analyzed based on Points of Interest (POI) from Internet maps by using frequency density and type ratios and kernel density estimation. Further, the results were compared via visual interpretation based on remote sensing data. Results show that a planning and management system for altered urban land function is important to ensure urban renewal. The overall distribution pattern of urban functional land during both phases showed a circular regional distribution. Mixed-function and single-function lands present a "center-peripheral" distribution pattern. Specifically, the mixed-function lands were mainly distributed in the center of urban area, while the single-function lands were distributed in the peripheral regions along the mixed-function land, and outnumbered the mixed-function lands. Both single-function and mixed-function lands expanded outward, and the total functional land was increased by 39.04%. Changes in urban land function were required for urban economic transformation and upgrade, improvement of the residents' quality of life and ensuring urban ecological environment. The scale and number of single-function land use types increased. Specifically, the scale and number of industrial lands showed the most significant change, accounting for 54.45% of the total change. The green land and square land use as well as the land used for traffic facilities increased significantly, while residential land, public management and public service lands, and lands for business service facilities increased insignificantly. Changes in urban land function were mostly attributed to economic and intensive use of urban land resources, thus leading to optimal configuration and layout of land spaces. The main types of mixed-function land use were unchanged, whereas the quantitative proportion was increased by 16.85%. The scale and number of mixed-function land including green land and square land or lands for traffic facilities increased partially. A confusion matrix was established by comparing randomly selected samples with actual land use in high-resolution images. The overall accuracies of POI data in the two phases were 79.01% and 73.14%, respectively. The results of identification were relatively accurate. Based on comparison with RS identification, it is feasible to analyze the changes in the function and characteristics of single-function and mixed-function lands in cities based on refined extraction and division of POI data. Further, this approach facilitates layout planning of mixed urban functions in future and increases land utilization. Based on the analysis of changes in urban land function and characteristics in built-up areas of Changsha, three suggestions were proposed from the perspective of future urban development, mixed layout of land functions, green infrastructure construction and urban marginal regions. First, the mixed layout of land functions should be reinforced and the land utilization should be increased. Second, the green infrastructure and the comprehensive carrying capacity of cities should be enhanced. Third, urban marginal management should be strengthened and the disordered expansion of cities should be prevented.

Key words: urban land use function, POI data, RS interpretation, functional change characteristics, Changsha built-up area