## 5 Results and Discussion
### Spatial Heterogeneity Effecton Metro Ridership  
Previous studies have mostly used Partial Dependence Plot (PDP) dependency maps to study the impact of the built environment explanatory variables on metro ridership from a global perspective [3; 21]. However, existing research has demonstrated spatial heterogeneity in the influence of the built environment explanatory variables on metro ridership [17; 18] and that the influence of built environment explanatory variables on metro ridership varies depending on the station's location. Therefore, this study links SHAP values to metro stations and visualizes them. In this section, the top three global influences of the explanatory variables are still selected for spatial heterogeneity analysis. The results of the visualization of metro station SHAP values are shown in Figure 8.  
For metro stations inside the 4 th Ring Road, the number of metro stations with positive and negative SHAP values for the number of entrances and exits are roughly evenly divided. The metro stations with high negative SHAP values are mainly located in the northern part of the 4 th Ring Road. The likely reason for this is that these metro stations are saturated with passengers, and further upgrading the number of entrances and exits to the metro stations will not enhance metro ridership. In addition, the metro stations with positive high SHAP values are mainly located in the southeastern part of the 4 th Ring Road (Figure 8a). For the mixed utilization of land, there are more negative SHAP metro stations than positive SHAP metro stations (Figure 8b). This demonstrates that for most metro stations inside the 4 th Ring Road, the mixed utilization of land dampens metro ridership. The reason for this may be that these neighborhoods are functionally mixed. However, it is a fact that where there is a high density of residential areas, there is also a high level of ridership at metro stations, and an excessive mix of land use reduces the number of residential areas. In addition, metro stations with negative SHAP values are clustered inside the 4 th Ring Road. Therefore, when urban renewal is carried out later, the agglomeration area of metro stations with negative SHAP values can be considered uniformly. For the density of bus lines, the number of metro stations with negative SHAP values is much greater than the number of positive SHAP value metro stations (Figure 8c). This demonstrates that the density of bus lines has a dampening effect on metro ridership for most metro stations inside the 4 th Ring Road. There is also a strong concentration of positive high SHAP metro stations, with positive high SHAP metro stations concentrated in the southeast and southwest inside the 4 th Ring Road. Figure 8: _Cont._  
For the metro stations outside the 4 th Ring Road, the number of public service facilities with positive high SHAP values metro stations are clustered in the north and east of outside the 4 th Ring Road (Figure 8d). Combined with Figure 1, the ridership at the metro stations with positive high SHAP values is high, and we can reduce the ridership at the metro stations by reducing the number of public service facilities. Also, most of the stations with high negative SHAP are concentrated at the end of the metro line (Figure 7d). The possible reason is that these metro stations are located in suburban areas, where there may be some large infrastructure and public service facilities, and these facilities lead to fewer residential neighborhoods. The metro stations with positive building density SHAP are mainly concentrated at the end of the metro line (Figure 8e). And, the ridership of these metro stations are low, so we can enhance the ridership of these metro stations by increasing the building density. In addition, the stations with high negative SHAP have a strong agglomeration effect, especially in the north of the 4 th to 5 th Ring Road and the southeastern outside the 4 th Ring Road (Figure 8e). And, these metro stations can be considered unified as a solution to regional problems.