# How Does the Built Environment Affect Mechanical Parking Space Planning: A Case Study in Xi'an City
## 5 Results
### Global Interpretability  
The relative importance of the variables obtained in Python is shown in Figure 2. The relative importance of a variable is the predicted contribution of an independent variable to the dependent variable relative to other independent variables. The higher the relative importance, the greater its effect on the dependent variable. Land use mix (46.2%) and distance to CBD (38.2%) (Bell Tower in Xi'an) are two of the most important variables affecting the mechanical parking spaces ratio. Followed by the variables architecture type (5.4%), network density (4.2%), and fee (3.2%). [PERSON] et al. [29] proposed that proximity to the city center is the second most important factor and that intersection density has the lowest impact on parking demand, which is consistent with our study. The ALE plots show a non-linear and threshold effect of factors on the MPS ratio. The blue line indicates the value of the independent variable. The denser the blue line, the \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Variables** & **Description** & **Min** & **Max** & **Mean** & **Std.** \\ \hline \multirow{3}{*}{Distance to CBD} & The distance from the center point of the buffer & \multirow{3}{*}{0.21} & 29.51 & 7.92 & 4.29 \\  & zone to CBD (Bell Tower) & & & & \\ \multirow{3}{*}{Fee} & Parking fee & 0 & 10 & 2.11 & 1.48 \\  & The parking lot is located in Xi’an (Inside the & \multirow{3}{*}{1} & \multirow{3}{*}{4} & \multirow{3}{*}{2.94} & \multirow{3}{*}{0.91} \\  & Ming City Wall, Ming City Wall-Second Ring, & & & & \\ \multirow{3}{*}{Area} & Second Ring-Third Ring, and Third Ring & & & & \\  & Outside). & & & & \\ \multirow{3}{*}{Architecture type} & 1. Hotel; 2. Public; 3. Temporary; 4. Business & \multirow{3}{*}{1} & \multirow{3}{*}{9} & \multirow{3}{*}{5.76} & \multirow{3}{*}{2.71} \\  & office; 5. Relics scenic spot; 6. Housing; 7. & & & & \\ \cline{1-1} \cline{5-5}  & Comprehensive business; 8. Hospital; 9. Other & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: \(Cont.\)  
Figure 2: The relative importance of each variable. higher the frequency of that value. Figure 3a shows that the land use mix is positively associated with the MPS ratio. When the land use mix is less than 0.83, there is no obvious variation in the MPS ratio. While it exceeds 0.83, its effects are faced with a sharp increase. The distance to CBD is negatively associated with the MPS ratio, as shown in Figure 3b. It shows a threshold which is about 7 km. When the MPS ratio is less than 7 km, it faces a large slope. When it exceeds 7 km, the influence is minimal. The reason is that the land resources in the city center are scarce, and mechanical parking spaces are needed to improve the level of land use, meet parking demand, and improve turnover efficiency. Different architecture types have different effects on the MPS ratio (Figure 3c). The hotel, public, and temporary areas need more mechanical parking spaces. The network density has an extreme effect (Figure 3d). The higher or lower the density, the greater the impact on the parking rate. The road network in the city center is dense and the shortage of land requires mechanical parking spaces. The road network outside the suburb is sparse, and some large attractions, such as parks or commercial centers, have a high demand for parking. See from Figure 3e, the influence of bus stops on MPS ratios is positive and the threshold is 5 units/km\({}^{2}\). The higher the density, the higher the ratio, mainly because the higher the density, the more likely it is to be in the city center, and, therefore, the higher the requirement for the ratio. See from Figure 3f, the influence of fees on MPS ratios is positive and the threshold is 2.5 yuan/h. The higher the cost, the higher the rate. The main reason is that, on the one hand, the parking fee in the city center is high, and it is more likely to build mechanical parking spaces. On the other hand, the cost of a mechanical parking lot is higher than that of an ordinary parking lot.