Abstract: In recent years, major cities in mainland China have achieved rapid development in underground commercial space. The underground commercial space has become an important carrier and component of urban commercial activities. The rational layout of underground commercial space plays an essential role in a city's economic development and in meeting the needs of residents' consumption activities. Existing studies have primarily analysed the POI layout characteristics of commercial facilities in metropolitan areas and urban centres. However, there is a lack of relevant research on the distribution and evolution of commercial POI in underground space. Based on the POI data of Chengdu in 2015, 2018, and 2020,  POI point distribution of underground commercial spaces in the three major areas of North Railway Station, Chunxi Road, and Global Center was extracted using Python and GIS through nuclear density analysis and standard deviation data. The hotspot distribution, spatial organisation mode, spatial expansion direction, and business aggregation characteristics of the temporal and spatial evolution of the underground commercial space in the typical commercial district of Chengdu were investigated using ellipse and other methods. Developments of the three major districts between 2015 to 2020 were compared in terms of transportation accessibility, industrial restructuring, and the stock of development by using multi-source big data such as urban rail transit passenger flow, bus station density, occupational and residential facility density, floor area ratio, housing price. The evolution mechanism of underground commercial space was discussed in combination with Chengdu's spatial planning and development strategy. It is expected to provide a scientific basis and theoretical support for underground commercial space's rational layout and development.
　　The results show that:①The underground commercial space in the three major areas expands from the centre to the periphery, and the characteristics of corridor agglomeration and scattered point expansion are apparent. The underground commercial space agglomeration tends to be multi-centred and tend towards clusterisation. The underground commerce of the North Railway Station has developed from a single core to a dual-core structure; the Chunxi route "shaft belt" has evolved into a "networked" spatial structure, while the global centre area maintains a "multi-core" spatial structure. The underground commercial space and the rail transit station have three vertical organisational modes: close proximity, channel connection and shopping streets connection.②The underground business space in Chunxi Road Area shows a decline in catering and an increase in shopping and life services. The global centre is a growth type of life services, whereas the North Railway Station Area is a growth type of shopping. ③The standard ellipse characteristics of the underground commercial space distribution in the North Railway Station Area and Chunxi Road Area have undergone more significant anisotropic changes. In contrast, the standard ellipse characteristics of the global centre attenuated gradually. The development of underground commercial space is multi-directional and uniform. Complexes and high-density development areas are the main hotspots for expanding underground commercial spaces. ④Consumers, governments, and enterprises are the main development layers of underground commercial space. Under the internal interaction of demand traction (consumer)-control and guidance (government)-adaptation to the market (enterprise), the logic and mechanism for underground space expansion utilise improvement of rail accessibility as the "spatial impetus", vertical expansion of commercial complex as the "space carrier" and the downward excavation of inventory space as "space basis" is formed. Finally, the optimisation strategies for developing underground commercial complexes based on the urban railway system and the underground business district based on diversified locations and consumption habits were proposed by combining the evolution laws and mechanism of underground commercial spaces in Chengdu. 

Key words: underground commercial space, hotspots, spatial and temporal evolution, POI, evolution mechanism, Chengdu

摘要： 地下商业空间是城市商业活动的重要载体与组成部分，其合理化布局对发展城市经济、满足居民消费需求发挥着重要作用。基于2015年、2018年、2020年的成都市POI数据，运用Python、GIS提取火车北、春熙路、环球中心三大片区的地下商业空间历年POI点位分布。通过核密度分析、标准差椭圆等方法，解析成都市典型商圈的地下商业空间时空演化规律与机制。结果表明：①三个片区的地下商业空间平面布局均表现为廊道集聚和散点扩张特征明显，地下商业空间集聚趋于多中心与簇群化，竖向组织形成了紧邻式、通道连接式、商街连接式三种模式；②春熙片区地下商业业态呈餐饮占比衰减，购物与生活服务增加的趋势，环球中心为生活服务类增长型，而火车北为购物增长型；③火车北站与春熙路片区地下商业空间分布的标准差椭圆特征向异性变化更为显著，而环球中心则为衰减状态，地下商业空间发展呈多向均匀式布局发展；④交通可达性提升、产业空间重构、存量空间开发等是成都市地下商业空间的演化重要驱动因素。

关键词: 地下商业空间, 热点区, 时空演化, POI, 演化机制, 成都