## 3 Research Methods
### Construction of Variable Set  
The spatial efficiency elements of the station area include four aspects, namely, land, transportation, social efficiency, and environmental efficiency. The selection of variable indicators in this study involves four aspects: land efficiency, transportation efficiency, space efficiency, and social efficiency. Regarding variable selection, the theoretical analysis method, the use frequency statistical method, and the expert consultation method are used for index screening. The theoretical analysis method provides a comprehensive analysis of the connotation description of the current rail transit station area spatial efficiency and selects indicators with important characteristics. The use frequency statistical method is used to conduct statistical analyses of surveys on rail transit station areas and papers related to spatial efficiency. This method is used to filter out high-frequency indicators. The expert consultation method is used to gather expert opinions on the basis of the initially formed survey indicators of rail transit station area spatial efficiency to optimize the indicators, thus providing a higher degree of recognition. Considering the objectivity, availability, representativeness, and effectiveness of the data, this paper constructs the input variables based on the evaluable objectives. The following input variables are assessed: X1, total land area; X2, total building area; X3, green space and square land area; X4, number of bus routes; X5, number of underground parking facilities; X6, number of commercial stores; X7, number of station area rail transit complexes; and X8, surrounding population size (ten thousand people). The total land area is the land area included within an 800 m radius from the rail transit station. The total building area is the building area of the land that falls within a radius of 800 m from the rail transit station. The green space and square land area is the area of all public squares and concentrated green spaces within an 800 m radius from the rail transit station. The number of bus routes is the sum of the number of bus routes in the station area. The number of underground parking facilities is the number of underground parking lots in the station area. This metric reflects the general situation of the station area's traffic service level and the degree of traffic convenience. The number of commercial stores is calculated based on the retail POI points in the station area. A station area rail transit complex refers to a commercial complex connected to a station by an underground passage. The surrounding population size is the sum of the resident population and the number of employment positions in the station area. Output variables include Y1, land diversity; Y2, subway passenger flow; Y3, CO2 absorption capacity; Y4, road network density; Y5, parking space utilization rate; Y6, standard price of commercial land; Y7, rent level; and Y8, the number of employment positions. Figure 3: Construction of the evaluation indicator system. Among them, the land mix (Equation (3)) can describe the richness and complexity of land use in the station area. The standard price of commercial land is obtained from the Notice on Publishing the Standard Land Price of Xi'an Urban Area [37]. Subway passenger flow selects the data of the day with the largest passenger flow during the research period. The road network density is obtained by dividing the total road length by the total land area of the station. The density of underground parking facilities is obtained by dividing the total number of underground parking facilities by the total station area. The green space rate is obtained by dividing the total green space area within an 800 m radius from the rail transit station by the total land area of the station area. The rent level is the average rent of shopping malls and shops within an 800 m radius from the rail transit station. The number of employment positions is the sum of the number of employment positions of various industries in the station area.