## 2 Materials and Methods  
### Location, Views, and Activities of the Study Site  
Given the importance of open space to a residential area, as shown in Figure 2, the Shenzhen OCT ecological square was selected as the study site for this research due to its representation of life in a Chinese metropolis. Shenzhen is a typical Chinese metropolis with nearly 18 million people. However, it was once a sparsely populated territory occupied by several scattered villages. The city has been steadily developing since it was designated as one of the first Chinese special economic zones and as the window of the National Economic Reform that started in 1979. Since the 1980s, the city has experienced a tremendous transformation from a fishing village to a bustling metropolis in just over 30 years. In this urbanization process, the population has grown from thousands to nearly twenty million [40].  
Amidst rapid urbanization, hundreds of residential areas have been developed in Shenzhen, one of which is the Shenzhen OCT. After nearly 40 years of development, the OCT has been forged as a high-density residential area comprising several communities with approximately 80,000 inhabitants and an area of 0.57 km\({}^{2}\). The OCT ecological square is the main public open space in the residential area. It is open not only to the OCT inhabitants but also to the public outside the residential area. The square provides a wide range of functions to support holding various activities and events for the inhabitants. The OCT spans an area of 4.6 hectaes [41]. The age range of the residential buildings in this area spans from the 1980s to the 2020s. Currently, the inhabitants of the OCT cover a broad social group, including estate property owners and tenants with a variety of social/demographic backgrounds.  
Figure 1: The research framework of the present study.  
As a representative of China's fast-paced urbanization, studying the soundscape of the OCT ecological square can provide valuable insights and useful guidelines for the sustainable development of urban residential areas in the design stage. The location of the study site, the Shenzhen OCT ecological square, is illustrated in Figure 2, which was mapped with ArcGIS (Ver. 10.2, ESRI, Redlands, CA, USA). In Figure 2, some territorial features and the locations of Shenzhen and the study site can be seen. It also shows that Shenzhen is a coastal city in Southern China near the South China Sea.  
Figure 3 shows the divisions of the square with images. As sounds, landscape features, and related perceptual factors are important in the definition of a soundscape [42], the study site was specifically visited and observed in terms of sound sources, landscape elements, and the behaviors of the users. It was found that the square contained four different blocks due to their various sounds, landscapes, and spatial functions. According to in situ observations, the site could be roughly divided into four blocks, namely BLK-I, BLK-II, BLK-III, and BLK-IV, as shown in Figure 3.  
The distance from a block to the square's entry and neighborhood attributes are shown in Table S1. Based on the distance from a block to the square's entry, the blocks were consequently named Block I (BLK-I, with the spatial function of exercise), Block II (BLK-II, with the spatial function of relaxation), Block III (BLK-III, with the spatial function of communication), and Block IV (BLK-IV, with the spatial function of restoration), where BLK-I was nearest to the entry while BLK-IV was furthest.  
Figure 2: Location of the Shenzhen OCT ecological square.