## 2 Materials and Methods
### Methodology
#### 2.4.3 Selection of Subjective Perception Dimension Indicators  
People's activities within street spaces are motivated by their needs, with specific actions grounded in their spatial perception and assessment of safety and convenience [47]. Regarding subjective perception, elements such as street greenery and sky visibility impact users' psychological responses to varying extents and play a crucial role in fostering comfort. Additionally, the proportion of motor vehicles on the street is closely associated with users' sense of security, while the number of traffic signs correlates with traffic complexity; higher vehicle ratios and more signs tend to diminish users' sense of safety. Safety and comfort represent foundational physiological needs, whereas social interaction addresses higher-level psychological needs [48]. Streets serve as important social spaces, where greater enclosure correlates with an increased social index. In summary, individuals' perceptions of street space can be categorized into three primary aspects: comfortableness, safety, and social connectivity. 1. Comfortableness  
The green visual index and sky visibility index were chosen to assess the comfort level of street space. Through the analysis of street view images, the proportion of green vegetation area is extracted and defined as the Green Visual Index (GVI), and the calculation formula is as follows (6):  
\[GVI_{n}=\frac{G_{n}}{A_{n}}=\frac{\sum_{i=1}^{i}{g_{i}}}{\sum_{i=1}^{i}{a_{i}}}, \tag{6}\]  
where \(G\) represents the total number of pixels occupied by trees, vegetation, and other green elements in the designated streetscape image, specifically the sum of pixels corresponding to individual vegetation components within the image; \(A\) denotes the total number of pixels present in the streetscape image. The Sky Visibility Index (SVI) quantifies the number of pixels representing the sky area from the observer's viewpoint; a higher SVI indicates a more comfortable visual experience, and the calculation formula is as follows (7):  
\[SVI_{n}=\frac{\sum_{i=1}^{i}{v_{i}}}{\sum_{i=1}^{i}{a_{i}}}, \tag{7}\]  
where \(v_{i}\) represents the number of pixels within the \(i\)-_th_ sky surface domain of the image and \(a_{i}\) denotes the total number of pixels in the \(i\)-_th_ streetscape image. 2. Safety  
The proportion of motorized vehicle elements (including buses, cars, and public locomotives) identified in the semantic segmentation results of the streetscape image servesas an indicator of the Vehicle Interference Index (VII); a higher VII value correlates with decreased street safety, and the calculation formula is as follows (8):  
\[VII_{n}=\frac{C_{n}}{R_{n}}, \tag{8}\]  
where \(C_{n}\) denotes the number of pixels corresponding to motor vehicle patches identified in the street view image, while \(R_{n}\) represents the total number of pixels allocated to motor vehicle lanes within the entire image. The Interface Transparency Index (ITI) serves as a crucial indicator of road space safety, enabling a comprehensive assessment of road safety conditions through the quantitative analysis of the number of signals and signs present on the road, and the calculation formula is as follows (9):  
\[ITI_{n}=\frac{T_{n}}{A_{n}}=\frac{\sum_{i=1}^{i}t_{i}}{\sum_{i=1}^{i}r_{i}}, \tag{9}\]  
where \(T_{n}\) denotes the total number of pixels corresponding to traffic facilities and other markings within the street view image and \(R_{n}\) represents the total number of pixels encompassing the entire street space; the ITI value reflects the density of traffic facilities. A higher ITI value indicates greater complexity in traffic conditions, which corresponds to reduced safety levels. 3. Social connectivity  
This paper assesses the socialization of street spaces through the lens of the crowd agglomeration index and the social interface index.