*3.4. Depth Analysis*

The streets in the Sishengci historic district are narrow. They are used for social interaction on foot or by bicycle, so the streets are public spaces for people to carry out their activities. The analysis is carried out from the depth value, which indicates the minimum number of spatial transitions required to reach other spaces in a system. The higher the depth value, the less accessible the space is, and the lower the intensity of human activities in this space. In the depth value map (Figure 6), the axial lines with lower depth values are mainly located in the center of the district, Xinglong Street, Huaxingshang Street, Huaxingzheng Street, Huaxing East Street, Fanku Street, Rushian Street, Fuzi Street, and Wangfu Street, which are road spaces with higher accessibility. This axial line divides the district, and this road division pattern helps to disperse people's flow, which is in line with

the development law of the human living environment. The axial lines with higher depth values are concentrated and distributed in the same area as the overall higher integration range, indicating that these spaces of Xinglong Street, Huaxingshang Street, Huaxingzheng Street, Huaxing East Street, Fanku Street, Rushian Street, Fuzhi Street, and Wangfu Street are closely connected to the center of the district and easily accessible.

**Figure 6.** Depth value map.

#### *3.5. Intelligibility Analysis*

Sishengci historic district is the starting point of Western medicine in Sichuan, the origin of modern medicine in Sichuan, and once made a significant contribution to the life and health of the Sichuan people. In terms of intelligibility analysis, intelligibility is a variable that represents the relationship between connectivity and global integration, and its value is expressed by the linear regression coefficient *R*<sup>2</sup> between these two types of variables. Intelligibility is used to represent and index the readability of the overall space based on the local space. It means the amount of connected space seen from space can be a helpful guide to integrating the space that we cannot see. It can be used to measure whether the local spatial structure seen contributes to the understanding of the overall spatial system. An unintelligible environment can be interpreted as a rupture of this cognitive and grouping relationship. In the intelligibility analysis, the connectivity was selected for linear regression analysis with the global integration, and the intelligibility of the axial lines system was derived from the *XY* scatter plot (Figure 7) to quantify the spatial relationship between the historic district locally and as a whole. In the figure, *X* denotes global integration, *Y* denotes connectivity, and *R*<sup>2</sup> denotes intelligibility. The red dots at the top right indicate the axial lines with higher intelligibility, while the blue dots at the bottom left indicate axial lines with lower intelligibility.

The scatterplot shows that the axial lines represented by the red dots with high intelligibility are formed by the connection of Xinglong Street, Huaxingshang Street, Huaxingzheng Street, Huaxing East Street, Fanku Street, Rushian Street, Fuzi Street, and Wangfu Street. These axial lines are surrounded by critical public spaces, in line with the axial lines in the center of the district. They occupy an important position in the district and are iconic. The intelligibility value of the Sishengci historic district is about 0.86, which is high. It shows that it is easier to perceive the overall spatial system of the historic district from the local space, the recognition of the streets is high, and its street space presents a regular form. During the development process of the historic district, attention should be paid to the conservation of the texture and natural form of the historic district.

**Figure 7.** Intelligibility scatterplot.
