**1. Introduction**

Rural settlement is the key research field of rural geography. It is a complex system composed of social economy, natural ecology and other subsystems. It has a certain scale, structure, form and function, and has the main characteristics of complexity and dynamics [1,2]. Since the reform and opening up, with the rapid industrialization and urbanization process in China, the interactive flow of urban and rural resource factors has accelerated, the structure of production factors in rural areas is changing, and the development and evolution of rural settlements are undergoing rapid transformation. Rural settlements are also gradually shifting from "homogeneous" to "heterogeneous", and the transformation and development of rural settlements present a variety of scenarios [3,4]. To promote the implementation of the rural revitalization strategy and build a beautiful countryside suitable for living, working and visiting, the development of rural settlements is an important basis for rural revitalization [5]. Therefore, exploring the spatial characteristics, influence mechanism and reconstruction path of rural settlements in typical regions is a realistic proposition under the background of rural revitalization.

**Citation:** Zhang, R.; Zhang, X. Distribution Characteristics and Influencing Factors of Rural Settlements in Metropolitan Fringe Area: A Case Study of Nanjing, China. *Land* **2022**, *11*, 1989. https://doi.org/10.3390/ land11111989

Academic Editors: Yongsheng Wang, Qi Wen, Dazhuan Ge and Bangbang Zhang

Received: 9 October 2022 Accepted: 3 November 2022 Published: 6 November 2022

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Rural settlement geography is the main branch of rural geography. With the development and transformation of rural geography, the focus of rural settlement geography research is also constantly changing [6]. In the 18th century, geographers began to explore the relationship between people and land in rural areas. In this process, they began to study rural settlements, mainly involving the origin, distribution, type, evolution of rural settlements and their relationship with the environment [7–9]. After the 1950s, research in developed countries began to focus on spatial classification and measurement, research on rural sustainable development and the impact of human decision-making behavior on rural settlements [10–13]; the research content was constantly enriched. By the 1990s, under the influence of many philosophical trends, especially postmodernism, existentialism, idealism, humanistic geography, structuralist geography and critical realism geography, the research paradigm of rural geography in western countries began to transform to the social human direction at this stage [14–16]. With the rapid development of rural industrialization and urbanization, the rural settlement system and spatial structure have been constantly changed. The research on rural transformation and reconstruction has attracted scholars' attention, involving rural economy, society, space and other aspects [17–20]. In terms of distribution characteristics, landscape index, spatial syntax, fractal theory and other research methods are used to study the distribution characteristics of rural settlements from different aspects. For example, Hudson [21] analyzed the distribution system of rural settlements in Iowa on the basis of central place theory and diffusion theory; Weisler [22] studied the settlement space structure of Polynesian bacteria states from the perspective of historical evolution; Conrad [23] used remote sensing technology to measure the expansion of the spatial scale of rural settlements in Uzbekistan; Gallarati [24] combed the context of landscape and environment at various scales and studied the space and type of rural settlements. The research focused on the spatial layout of settlements [25], rural land use [26], settlement scale and form [27], etc. In terms of influencing factors, scholars in western countries started to study the influencing factors of rural settlement layout early. As early as the 1940s, they carried out a discussion on the relationship between rural settlement distribution and geographical environment [28]. With the development of social economy, the focus of research has gradually shifted to the human, economic and social directions, paying more attention to the relationship between population density and rural settlement distribution [29], the relationship between economic transformation and rural settlement distribution [30], the relationship between policy system and rural settlement distribution [31], the relationship between farmers' behavior and rural settlement distribution [30]. The research on influencing factors of rural settlement has experienced a change from focusing on natural factors to comprehensively considering various factors, such as natural, social, economic and cultural factors, and the perspective of research tends to be comprehensive.

The study of rural settlements in China started relatively late. Influenced by the academic research trend of geography in western countries, Lin [32] and other geographers of the older generation began to study rural settlements in the 1930s. Summarizing the research results of rural settlements in China, the study can be roughly divided into four stages: embryonic start (before 1949), preliminary development (1949–1978), rapid development (1978–2000), transformation and reconstruction (2000-present) [33–35]. Taking a general view of the research achievements related to rural settlements in China, a summary was made from the three dimensions of research contents, methods and scales. (1) In terms of research contents, the research mainly focused on the spatial pattern [36,37], evolution characteristics [38], influencing factors [39] and optimal regulation [40] of rural settlements. (2) In terms of research methods, multiple methods such as GIS spatial analysis [41], econometric analysis model [42] and field investigation method [43] were applied to the spatial analysis of rural settlements, showing a trend of cross-integration of multidisciplinary research methods. (3) In terms of research area, the current research mainly focused on the Pearl River Delta [44], Yangtze River Delta [45], Beijing-Tianjin-Hebei [46], etc. The research area mainly focused on the developed coastal areas in the east, and the typical areas (hilly area [47], loess area [48]) were also involved. Some scholars have also paid attention to

the spatial pattern of rural settlements in metropolitan areas [49,50]. Through the review, it can be found that the current research focused more on the description of the spatial pattern characteristics of rural settlements. The discussion on the spatial characteristics and formation mechanism of rural settlements in different typical regions was relatively weak.

As a transitional zone between urban and rural areas, the metropolitan fringe is faced with an overall transformation of economic, social and spatial structures. However, the spatial evolution of rural settlements located in the metropolitan fringe was influenced by rural urbanization. Compared with the traditional rural settlements, the rural settlements located in the metropolitan fringe were affected by the radiation and driving effect of the urban core area, and their spatial characteristics were characterized by complexity and diversity [51]. Nanjing is located in the Yangtze River Delta urban agglomeration, which is a metropolis in the coastal development area of eastern China. In the process of rapid urbanization, the rural settlements in the urban fringe are facing transformation and reconstruction, which can better reflect the characteristics of the rural settlements in the metropolitan fringe. In view of this, this paper chose Nanjing as a typical case, based on the interpretation of remote sensing image, using R statistics, kernel density analysis, hot spot detection analysis and semi variogram function, the paper analyzed the distribution characteristics and influencing factors of rural settlements in the metropolitan fringe area. The objective of these analyses is to address the following research goals: (1) What are the distribution characteristics of rural settlements in the metropolitan fringe? (2) What are the factors affecting the distribution of rural settlements in the metropolitan fringe? The research structure of this paper is as follows (Figure 1).

**Figure 1.** Theoretical analysis framework.


#### **2. Materials and Methods**

#### *2.1. The Study Area*

Nanjing is located in the eastern part of China, the lower reaches of the Yangtze River and the coastal areas near the Yangtze River. It is an important central city in the eastern part of China, an important gateway city for the development of the central and western regions driven by the Yangtze River Delta radiation, and an important node city for the strategic intersection of the eastern coastal economic belt and the Yangtze River Economic Belt. Nanjing covers an area of 6587.02 square kilometers, with a built-up area of 868.28 square kilometers. By 2021, the permanent resident population was 9.4234 million, and the urban population was 8.1889 million, with an urbanization rate of 86.9%. The GDP reached 1635.532 billion. Nanjing as one of the important cities in Yangtze River delta, with the rapid urbanization, rural industrialization, and promote the new rural construction, the dramatic changes in rural landscape, the region characteristics of traditional countryside gradually shift, a shift from rural to urban settlements, space from scattered to gather, lead to the new pattern of rural human settlements faces differentiation restructuring. In addition to its own development, rural settlements in the hinterland of the metropolis are also affected by the radiation of the central city, and their spatial characteristics are characterized by diversity and complexity. In view of this, this paper choosed Nanjing as a typical case to analyze the spatial distribution characteristics and influencing factors of rural settlements, which was typical for studying the development of rural settlements in the metropolitan fringe area (Figure 2).

**Figure 2.** Location map of Nanjing.
