**3. Overview of the Built-Up Area of Chongqing's Main City's Spatial Changes**

#### *3.1. High-Speed Traffic and Increased Road Density*

The movement of people and things that require transport between and within the cities of Chongqing has risen more often as a result of modernization and urbanization, which is a sign of increasing mobility [45,46]. A city cannot grow in size without its dynamic component, which is traffic [47]. Since early-modern times, the transportation system which is the carrier of material flow—has seen drastic changes in terms of transportation technology, methods, and network. After the liberation, the waterway-based transportation situation from the early stages of the country's founding was gradually changed, and after strengthening the construction of highways and railroads, the connection between Chongqing and the neighboring cities was gradually tightened (Figure 4), all in keeping with the general trend of the evolution of the city's external transportation.

**Figure 4.** (**a**) The evolution of transportation between Chongqing and the surrounding cities from 1940s to1980s; (**b**) The evolution of transportation between Chongqing and the surrounding cities from 1980s to 2010s; (Source: Historical maps, Chongqingshizhi, Google Earth, etc.).

Urban traffic has risen in volume as a result of modernity, population growth, economic development, and the concentration of a large number of people and cars inside the city, while urban sprawl has increased the distances people must travel to go anywhere in the city. Changes in intra-city transportation modes and technologies have resulted from rising intra-city mobility, while the intra-city transportation network system has evolved to meet the demands of urbanization in terms of land use, traffic, and other factors [48]. The expansion of new urban paths that new modes of transportation rely on, such as the construction of high-capacity, quick, and efficient railways and elevated railways to address the issue of high hills and steep slopes in Chongqing (Table 3), can be summed up as the first change in the urban transportation network. The second change is the continuous widening of inner-city roads and the growing density of the population. The complexity of the transportation system has increased as a result of the diversity of traffic; therefore, the organization of urban transportation is more three-dimensional and systematic [49].


**Table 3.** Development of subway in Chongqing (Source: the National Bureau of Statistics, Chongqing Shizhongquzhi).

Because of its location at the confluence of two major rivers, Chongqing has always relied heavily on the transportation services provided by its ports. After the start of the War, ferries emerged in response to the resulting population boom. Before the 1960s, traveling from one side of the city to the other required using the waterways that crisscrossed it; however, after the construction of bridges over the rivers and cableways to the two rivers, faster and more convenient ways of crossing the rivers emerged, displacing the cross-river routes and, later, the more heavily trafficked downriver routes [50]. The new transportation methods changed the way people traveled around the city, and public water transportation gradually declined (Figure 5).

### *3.2. Spatial Expansion and Functional Area Transformation*

The built-up area of Chongqing's main city has recently shown a tendency for outward growth (Figure 6). Specifically, the data on Chongqing city's outward expansion were slow from 1956 to 1983, which was related to the overall national background of the time, and the growth rate accelerated from 1983 to 1997, which was the expansion of the urban spatial pattern brought about by the accelerated economic development of Chongqing city since the reform and opening up, and the built-up area grew rapidly from 1997 to 2007 (Table 4), and Chongqing as a municipality directly under the Central Government grew rapidly as a result [51]. Chongqing's development focused on the main city at first, and the city expanded to non-main urban areas in the later years, a manifestation of urbanization in the rural areas; this expansion continued in the years 2007–2017, but at a slower rate than in the decade before the direct administration. The city expanded to the west and south in its early years, but after the administration, with better land and greater urban development space reserves, the north became the major direction of urban growth.

**Table 4.** Change in the built-up area of Chongqing's main city (Source: Chongqing shizhi and the National Bureau of Statistics).


**Figure 5.** (**a**) Mukdo Routes and Ferry Routes on the Two Rivers in the Early 1940s; (**b**) Changes in the way the main city crossed the River from the 1940s to 1980s; (**c**) The contemporary way to cross the River; (Source: Own study).

As the city grew, the macroscopic land use arrangement changed, which in turn impacted the nature of urban life to some degree. Given the city's geography and traffic patterns before 1949, the city's industrial property was virtually evenly spread on the riverbank terraces. The vast majority of the inwardly relocated factories were constructed with only the water transportation conditions of the Jialing and Yangtze rivers in mind, without a thorough understanding of the conditions in Chongqing, with intertwined factory areas and residential areas, an extremely irrational layout, and an extremely uneven production distribution, with factories, monstrously concentrated on the banks of the river. New industrial zones formed on the south side of the city as the city's scientific progress led to the gradual evacuation of industrial land initially clustered on both sides of the Jialing and Yangtze rivers with an exceedingly inappropriate layout. Since the 1990s, the government has actively promoted and supported large-scale industrial development in order to achieve development goals. This has directly led to the priority growth of industrial land, and it is clear that the new periphery of the city is primarily an industrial zone. The city's infrastructure is progressively becoming more streamlined.

**Figure 6.** (**a**) The built-up area of Chongqing's main city in the 1940s; (**b**) The built-up area of Chongqing's main city in the 1980s; (**c**) The built-up area of Chongqing's main city in the 2000s; (**d**) The built-up area of Chongqing's main city in the 2010s; (Source: Resources and environment science data center of Chinese Academy of Sciences).
