## 3 Study Areas and Data Process
### Data Process
#### 3.3.2 Risk Assessment Experiment  
Considering the availability of data, the feasibility of practical operation, the scientific of index selection, and the specific situation of Shanghai, we select ten influencing factors, including land use type, water density, land subsidence rate, and accumulation, as well as population density, GDP per unit area, road density, building density, ground elevation, and green space density. The ten factors can be divided into four hazard evaluation factors and six vulnerability evaluation factors (Figure 4). In the quantitative analysis, the land subsidence risk evaluation scale ranges from [0,1] and can be divided into five levels, which are Lower, Low, Medium, High, and Higher (46) (as shown in Table 3). The hazard of land subsidence H includes four aspects (Figure 5). Land use types are closely related to human activities. Human demand for construction land increases during the urbanization acceleration process. Therefore, in the excavation and filling of surface soil during the construction of infrastructure, large buildings cause the load on the underground soft soil layer to exceed the bearing pressure, which can easily lead to soil compaction and surface subsidence. The extraction or perfusion of groundwater, the dense distribution of rivers, and the width and depth of rivers will change the formation stress, so that the surface height will rise and fall. The rate of land subsidence reflects the development degree of land subsidence under various external influencing factors, which is a description of the current situation of the area where land subsidence has occurred. The time series land subsidence results obtained in this study are used as an important factor index of the land subsidence risk in Shanghai (Shenghai, 2018). Figure 4: Factors related to risk assessment of land subsidence. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Type** & **0–0.2** & **0.21–0.4** & **0.41–0.6** & **0.61–0.8** & **0.81–1** \\ \hline
**Risk level** & Lower & Low & Medium & High & Higher \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Grade division table. The land subsidence vulnerability V includes six aspects. Cities are the concentration centers of the population, the economy, politics, transportation, architecture, and other factors, and the vulnerability to disasters is much higher than in nonurban areas. The six indices of population density, GDP per unit area, road density, green space density, building density, and ground elevation, were selected to comprehensively evaluate the vulnerability to land subsidence in Shanghai. The distribution of vulnerability evaluation factors is shown in Figure 6. The population density reflects the degree of urbanization, and the GDP per unit of area reflects the national economic situation of the region, both of which are usually proportional to the vulnerability to land subsidence. Generally, the greater the road density, the higher the vulnerability to land subsidence. Buildings are mainly industrial, commercial, and residential high-rise buildings, and a higher building density means a greater risk of disaster vulnerability. Land subsidence causes ground elevation loss, and ground elevation is the foundation of regional political and economic activities, which seriously affect people's lives, property safety, and production activities. Figure 5: Distribution of hazard factors of land subsidence in Shanghai city: (**a**) is the land use type of the study area; (**b**) describes the water density; (**c**) represents the total subsidence during previous 7 years; and (**d**) marks the vertical velocity. Finally, we use ArcGIS to rasterize all the collected vector data in the evaluation model and then normalize the statistical probability distribution of the samples between [0,1] (as is shown in Table 4).