**4. Identifying the Spatial "Dynamic Layering" of Chongqing's Parent City**

#### *4.1. Modernization of the Transportation Network in the Parent City*

Chongqing's ancient Yuzhong Peninsula serves as a case study for this investigation of the city's evolution. Located in the heart of Chongqing city, which has served as a geographic and developmental epicenter at different times since antiquity, the Yuzhong Peninsula is bounded by the Yangtze River to the east and south and the Jialing River to the north. The sample of this investigation is drawn from an area bounded on the west by the Yangtze River Bridge, Shihuang Tunnel, and the Huahuayuan Bridge, and on the east by the Jialing River and the Yangtze River itself. This sample, covering an area of roughly 3.2 square kilometers, represents the oldest and densest part of Chongqing's urban landscape, and the process of change in this region since early-modern times is sorted out so that Chongqing's urban historical landscape may be studied in detail.

More than 240 alleyways and lanes, none wider than eight feet, existed in Chongqing in the early 1920s (Figure 7), and there was not a single road in or around the parent city. Less than 40 km of drivable roads existed in 1949; by the end of the 1980s, that number had increased to 72.84 km (Figure 7), and the overall length, road grade, and construction quality of drivable roads had all been improved [52,53]. With the construction of new roads such as the Jialing River Binjiang Road and the Yangtze River Binjiang Road, the

road network plan pattern of the river section has been altered, and the existing roads such as Minquan Road, Zhongxing Road, and Heping Road have been widened and repaired to become the city's main arteries. Furthermore, the Qiansimen Tunnel, Shihuang Tunnel, and Jiefangbei Underground Ring Road were built to alleviate ground pressure and demonstrate the tunnel's reasonableness as a mode of transportation in the mountain city of Chongqing [54], which is of great significance to the development of urban roads (Figure 7).

**Figure 7.** (**a**) Transportation network in the 1940s; (**b**) Transportation network in the 1980s; (**c**) Transportation network in the 2010s; (**d**) Eliminated lanes from the early-modern times to now. (Source: Historical maps, Chongqingshizhi, Google Earth, etc.).

After reform and opening up, the city sped up the pace of municipal construction, the existing street lane for extensive renovation and reconstruction, upgrading the quality of the road surface. This was a major change from the 1980s when the ladder lane was built to connect the upper and lower halves of the main city to supplement pedestrian access to the road. Because of the original streets' and lanes' low widths, some were combined and restored, while others were eliminated entirely. First, the junction of Binjiang Road and four bridges; second, the nodes of Jiefangbei, the nodes of the Changchangkou, and the nodes of Chaotianmen; and third, the nodes of North District Road and Kui Xing Lou [49,55].

Focusing on the variations in road texture patterns within the sample. The first is the changing of geometric characteristics of the traffic network (Figure 8), including the number, breadth, density of roads, etc. Arcgis provides access to the relevant data and imagery for this section. As the number of roads rises in density, it follows that more roads are being built. At the beginning of the nation, the road density of passable vehicles in the sample was 6.24 km/per km2 until the 1980s, when the road density of passable cars in the sample was 8.31 km/km2. The width of the three major roadways has risen dramatically, with the center arterial road increasing from the original 7 m to 32 m, the southern arterial road widening from 7 m to 33 m, and the northern arterial road widening from 10 m to 30 m [49–51], city streets are now three to five times as wide as they were back then. Technology advancement has made it possible to circumvent limits on urban road building. The construction of trunk roads along the river expanded the road space outward to the river, such as the Jialing River Binjiang Road with the rise in intra-city traffic [52,53], certain roadways were enlarged and built (Figure 8).

**Figure 8.** (**a**,**b**) Partial north main road change between the 1940s and the 1980s; (**c**,**d**) Partial south main road change between the 1940s and the 1980s; (**e**,**f**) Partial north main road change between the 1980s and the 2010s; (**g**,**h**) Partial south main road change between the 1980s and the 2010s. (Source: Open Street Map, Chongqing Street map, U.S. Geological Survey, Google Earth).

After that comes the information on integration, choice, connectivity, etc., all of which vary depending on the spatial topological structure. Depthmapx may be used to derive this information (Figure 9). Integration measures how easy it is to access both a single axis and the whole system as a whole [44]. It shows how well one street connects to others and how well one street blends into its surroundings. The results of the Depthmapx calculation clearly show that places closer to Jiefangbei have better traffic, a higher degree of integration, and a greater concentration of social and cultural life than those near rivers. As the contour line along the river is thick, and early road development is hampered by the city wall, the integration degree is low; this is connected to the " Fixation" [29] and the natural topography. The frequency with which people cross a street is a measure of the "transit traffic" in a given metropolitan area and may be inferred from the degree of its choice. If there is a lot of choice on the street, it means plenty of people walk there every day. Along the route, you can observe how the planned riverside road development would improve the flow of local traffic.

The parent city's transportation system is a dense grid created by zigzag roadways along the contour lines, which is a reflection of the layered character of the city's historical environment [56], which has developed mostly organically as a result of historical development. First, the transportation infrastructure has developed by increasing the traffic link to the city. Second, there has been an ongoing improvement to the parent city's internal traffic system, which has resulted in a traffic organization that spans all three dimensions. Roads in the parent city were scarce and displayed tree-shaped and radial structures during the early-modern era; they were features peculiar to the ancient city center, but they eventually gave way to irregular dense grid-like patterns when highways were improved. Thirdly, the micro-level road morphology of the parent city is characterized by a rise in both the width

and density of roads, as well as an increase in the quality of integration and accessibility of the road network and the openness of the street network.

**Figure 9.** (**a**–**c**) Integration in the 1940s,1980s and 2010s; (**d**–**f**) Choice in the 1940s,1980s and 2010s. (Source: Depthmapx screenshot).

#### *4.2. Transformation of Functional Space and Plan-unit*

From the historic maps of functional space transformation (Figure 10), since 1949, the parent city's functions have modernized and become more complex, and the internal function structure has been constantly adjusted to rationalize and develop into the tertiary industry, which now accounts for more than 90% of the output value in Yuzhong District. Specifically, the city's administrative functions have been weakened due to two factors: first, the commercial functions have taken the form of aggregation and have been developing into tertiary industries; and second, the administrative institutions that were originally gathered on Linsen Road in the lower half of the city have been relocated to Shangqing Temple. The residential function was strengthened to accommodate the increasing population, and commercial spaces were clustered around Chaotianmen, Jiefangbei, and Bichangkou [53]. The number of commercial trade form units increased, and the appearance of commercial form units became more modern [49,54,55].

According to the geometry of plan-units, the Mother City's block contours eventually changed from being rough to having tiny grid-like block contours, giving rise to the present dense network of small block contours (Figure 11). The phenomena of block profile redivision have occurred, and the tendency of "networking" has become more pronounced. The number of block contours inside the main block profile has increased, and the size of the block profile has been shrinking. "Construction first, then planning, then transformation" construction first "free growth" block shape, mixed with planning control, describes the whole process [56,57].

**Figure 10.** (**a–c**) Functional Space in the 1940s,1980s and 2010s; (**d**–**f**) Important buildings in the 1940s,1980s and 2010s. (Source: Historical maps, Chongqingshizhi, Google Earth and etc.).

The study of the turnover of components within plan-unit has been hampered by the absence of particular topographical and architectural drawings from the 1980s. In recent years, the facts and literature reveal that the turnover rate of architecture in the parent city has been more than 90% [58–60]. At the same time, the average height of buildings in the city has increased significantly, reaching roughly 4–5 stories by the end of the 1980s [47,48]. This is by far the most noticeable alteration to the period's interior space. The average height of a modern building is 33.8 m (roughly 10 stories), and the presence of numerous high-rise buildings has transformed Yuzhong District into a densely populated region characterized by its abundance of skyscrapers (the building plot ratio in this sample is 5.83, while the overall plot ratio is 3.29). These current data are derived from GIS.

Because of its dense population and rapid growth, the parent city has been redeveloped after its independence with Chinese emphasis on restoring its historic core. Therefore, there has been a process of inheritance and succession in the make-up of the plan-unit internally. Due to the stability of the street element and the fact that large-scale streets have stayed mostly unchanged since they were established, with the exception of expansion and reconstruction, the phenomena of succession can be seen in the block of plan-unit. Most of the internal structure of the plan-unit was inherited from the previous stage of slow development when small-scale progressive regeneration was the focus, and the later stage entered the large-scale regeneration stage, to modern commercial and commercial morphological units and modern residential morphological units. Early on in the large-scale renovation, most structures were demolished since their design was no longer compatible with the city's ongoing evolution.

**Figure 11.** (**a**) Block Distribution of the parent city in the 1940s and 1980s; (**b**) Block Distribution of the parent city in the 1980s and 2010s; (**c**) Transportation network in the 2010s; (**d**) Eliminated lanes from the early-modern times to now. (Source: Historical maps, Chongqingshizhi, Google Earth and etc.).
