## 3 Research Content and Methodology  
### Research Area  
Lanzhou is located in the northwestern part of China and represents the geometric center of the Chinese mainland. Its geographical coordinates range from 102\({}^{\circ}\)35\({}^{\prime}\)58\({}^{\prime\prime}\) to 104\({}^{\circ}\)34\({}^{\prime}\)29\({}^{\prime\prime}\) east longitude, and from 35\({}^{\circ}\)34\({}^{\prime}\)20\({}^{\prime\prime}\) to 37\({}^{\circ}\)07\({}^{\prime}\)07\({}^{\prime\prime}\) north latitude. As the capital of Gansu Province, Lanzhou functions as the political and economic hub of the province, comprising five urban districts and three county-level cities. The total land area of the city is approximately 13,085.6 square kilometers [4]. As reported in the \"Lanzhou Statistical Yearbook (2024)\", the permanent resident population of Lanzhou reached 4.4251 million by the conclusion of 2023. The city is characterized by a temperate semi-arid climate and comprises four distinct landform types: mountains, hills, intermountain basins, and river valleys. The topography exhibits a general gradient, with higher elevations in the southern region and lower elevations in the northern area. Additionally, the rivers within the city are part of the Yellow River Basin, contributing to its classification as a typical strip-shaped city [41; 42]. The administrative map presented in Figure 1 is sourced from the Autonavi Open platform, with this dataset having been updated in May 2021. The elevation data utilized in the DEM maps were acquired through the Baidu Map API interface. The block division lines, urban rail transit routes, and building contours illustrated in Figure 2 were also obtained via the Baidu Maps API interface. The locations of rail transit stations are determined based on their entrances and exits, as provided by the Baidu Map API; additionally, the geometric center of each station has been calculated and marked accordingly. Figure 1: Location of the study area. Figure 2: Research scope. The subject of this study is the 16 subway station areas in the central urban area of Lanzhou, located within (including along) the Chengguan District. The focus of our research is the Chengguan District, situated in the central region of Lanzhou, as illustrated in Figure 1. According to the \"Lanzhou Chengguan District Yearbook (2024)\", published by the Lanzhou Municipal Bureau of Statistics at the conclusion of 2023, the permanent resident population of Chengguan District represented 34% of the total population of Lanzhou in 2023, while its Gross Domestic Product (GDP) accounted for 34% of the city's overall GDP. The historical development of Chengguan District dates back to the founding of Lanzhou, rendering it the district with the largest population, the highest GDP, and the most extended construction history within the city. The topography of Chengguan District is shaped by the dumbbell-shaped river valley characteristic of Lanzhou, with the highest elevations of the two surrounding mountains reaching 2138 m. The central area of the district is predominantly flat, serving as the primary zone for residential and economic activities [43; 44]. This research domain serves as the principal hub for urban residents' activities in Lanzhou and is characterized by its advanced transportation infrastructure and the concentration of the majority of the city's urban rail transit stations. Due to challenges such as traffic congestion, a high incidence of accidents, and intricate road conditions associated with surface transportation, residents in the Chengguan District exhibit a significant demand for metro services and pedestrian mobility. Consequently, the urban vitality in this area is comparatively elevated [45; 46]. As depicted in Figure 2, the Chengguan District encompasses the entirety of Line 2 and the eastern terminus of Line 1. Additionally, both transfer stations within the municipal framework are situated within this district.