*3.2. Analysis of Influencing Factors*

Theoretically, the distribution of rural settlements is closely related to natural, economic, social, cultural and policy [60,61]. From the terrain, river system, traffic, economic and social development and policy factors, this paper mainly discussed the influencing factors of rural settlement distribution in the metropolitan fringe area.

### 3.2.1. Rural Settlements Distribution and Terrain Factors

Terrain condition is an important factor affecting agricultural production and life, as well as the basic factor forming the spatial pattern of rural settlements. According to the topographic characteristics of the study area, the altitude was divided into five levels: ≤100 m, 100~200 m, 200~300 m, 300~400 m and ≥400 m. The DEM raster data was carried forward into vector data according to the classification and analyzed by stacking with the distribution map of rural settlements. It revealed the internal relationship between the spatial distribution of rural settlements and the topography in the metropolitan fringe (Table 3). According to Table 3, within the altitude of 200 m, the distribution of rural settlements was the largest, and the proportion of the distribution of rural settlements gradually decreased with the increase in elevation. The patch density of rural settlements also showed an obvious decreasing trend with the increase in elevation. At the same time, with the increase in altitude, the distance index also gradually increased, indicating that the spatial distribution of rural settlements was more dispersed, and the density was weakening. It showed that the spatial distribution of rural settlements had a significant "altitude location directivity" in the metropolitan fringe area.

**Table 3.** Landscape index of spatial distribution of rural settlements at different altitudes.


#### 3.2.2. Rural Settlement Distribution and River System Factors

The distribution of river system is also an important factor affecting the spatial pattern of rural settlements in the metropolitan fringe area. This paper, based on the river system in Nanjing, calculated the shortest distance D from rural settlements (points) to rivers (lines), and divided the shortest distance D into six levels: D ≤ 500 m, 500 m < D ≤ 1000 m, 1000 m < D ≤ 1500 m, 1500 m < D ≤ 2000 m, 2000 m < D ≤ 2500 m, 2500 m < D ≤ 3000 m. By counting the percentage of rural settlement patches within different distance levels between rivers and rural settlements, the relationship between the spatial pattern of rural settlements and the distribution of river system was analyzed (Table 4). Table 4 showed that when the shortest distance D from rural settlements to the river was less than 1000 m, the total number of patches in rural settlements was 14,679, accounting for 80%; while when D was more than 2000 m, the total number of patches in rural settlements was 325, accounting for only 1.8%. Therefore, with the increasing radius from the river, the number of rural settlement patches showed a decreasing trend. The farther the distance from the river system, the less the distribution of rural settlements, and the spatial distribution of rural settlements showed a significant "hydrophilic distribution location directiveness".



3.2.3. Rural Settlement Distribution and Traffic Factors

Transportation is a prerequisite for commodity exchange, which has an important impact on the spatial distribution pattern of rural settlements in the metropolitan fringe area. The road is the axis connecting rural settlements, and the main channel for material flow and information flow transmission between settlements. With the increase in settlement scale, the demand for people flows and logistics between settlements will increase synchronously, and the density of road network between settlements will also increase rapidly. The convenience of transportation will also promote the expansion of settlement scale, and there is a certain mutual promotion between them [62].

In order to quantitatively reflect the relationship between traffic and rural settlements, based on ArcGIS10.2 analysis software, taking 500 m as the buffer radius, the road network was analyzed for buffer zone, and the 12 buffer zones obtained were superimposed, and analyzed with the layer of rural settlements in Nanjing to obtain the relationship between the distribution of rural settlements and the traffic network (Figure 8). Figure 8 showed that the first section (<1500 m) was a stable section, where rural settlements were mainly distributed. The second section (1500~4500 m) was a rapid reduction section, and the number and area of rural settlement patches were significantly reduced compared with the first section. The third section (>4500 m) was a slowly decreasing section, with a stable decline rate and a small number of rural settlements. Therefore, traffic factors played an important role in the distribution of rural settlements in the metropolitan fringe area, showing the characteristics of "road affinity" distribution.

**Figure 8.** The rural settlements in different distance zones to roads in Nanjing.

#### 3.2.4. Rural Settlement Distribution and Economic Social Development Factors

Economic social development factors are important factors affecting the spatial distribution of rural settlements, which are mainly reflected through agricultural population growth, industrial structure adjustment and urbaniztion [63,64]. In view of this, the paper selected 10 factors reflecting the economic social development and used factor analysis to reveal the economic social development factors that affect the spatial distribution of rural settlements in Nanjing. Firstly, SPSS18.0 software was used to conduct KMO and Bartlett tests. The results showed that KMO was 0.658, and Bartlett's *p* value was 0.0495 < 0.05, indicating the feasibility of factor analysis. Secondly, according to the data calculation, the characteristic root was greater than 1, and there were two common factors that met the requirements. According to Table 5, the cumulative variance contribution rate was 86.69%, so two common factors could be extracted to replace the original data indicators.


**Table 5.** Factor analysis results.

Table 6 showed that, the common factor 1 was mainly determined by indicators X1, X4, X9 and X10, which mainly reflected that agricultural population was the direct power to affect the distribution pattern of rural settlements. The premise of rural settlement construction was to meet the residential needs of farmers, so the increase in agricultural population and rural labor force was positively related to the size of rural settlement space. With the development of urbanization, the increase in the proportion of urban population was conducive to the regularization of the spatial distribution of rural settlements and promoted the development of rural settlements towards urban settlements. The common factor 2 was mainly determined by indicators X3, X5, X6 and X8, which mainly reflected the development status of rural economy. The level of rural economic development indirectly affects the spatial distribution pattern of rural settlements. With the development of rural economy, it provides economic guarantee for the development of rural settlements, the villages with the higher income of farmers have the larger area of rural settlements. Therefore, the distribution characteristics of rural settlements were mainly affected by agricultural population and rural economic development in the metropolitan fringe area.


**Table 6.** Selection of explanatory variables.

#### 3.2.5. Rural Settlement Distribution and Cultural Policy Factors

Cultural and policy factors play an important role in regulating the distribution pattern of rural settlements. Cultural factors include cultural customs, religious beliefs, etc, these are important components of China's traditional culture, which have a profound impact on the ideology of farmers and have an important impact on the distribution and form of regional rural settlements, which is the main reason for the formation and morphological evolution of many famous villages in Nanjing [65]. Policy factors had an important impact on the distribution of rural settlements in the metropolitan fringe. On the one hand, policy factors affect the distribution pattern of rural settlements through direct administrative mechanisms; on the other hand, it affects the behavior of residential location by indirectly acting on the behavior subject of farmers [66]. Land use planning, industrial structure adjustment and administrative division adjustment have a profound impact on the development and layout of rural residential areas in Nanjing. In recent years, with the implementation of the national strategy of rural revitalization, the spatial renovation policies of Nanjing, such as comprehensive land consolidation, the removal of villages and towns, and the construction of central villages, have affected the form and scale of rural settlements in Nanjing, it has promoted the transformation of rural construction space into a spatial layout form of large dispersion and small concentration. In addition, the adjustment of administrative divisions in Nanjing has changed the infrastructure level of some rural settlements, which had also become an important factor affecting the distribution and spatial reconstruction of rural settlements.

To sum up, the physical geographical environment (terrain, river, etc.) provided the basic conditions for the distribution of rural settlements in the metropolitan fringe area. With the continuous development of urbanization, traffic accessibility, agricultural population growth, rural economic development, cultural and policy have become the dominant factors for the distribution of rural settlements in the metropolitan fringe. The interaction of these factors has an increasing impact on the evolution and reconstruction of rural settlements in the metropolitan fringe in the future (Figure 9).

**Figure 9.** Impact mechanism of rural settlement distribution in the metropolitan fringe area.

#### **4. Discussion**

(1) Rural settlement is the evolution of the long-term integration of human and nature. Rural settlement is a complex system involving social, economic, ecological, resource and other factors. The distribution of rural settlements is characterized by regional differences. At present, the academic community has carried out research on the distribution law of rural settlements in different regions. Tang [67], Guo [68], Ma [69] and others have focused on the distribution law of rural settlements in northwest China. They have selected Yulin City in Shaanxi Province, Qin'an County in Gansu Province, Tongwei County in Gansu Province, such as case to carry out empirical research. They found that rural settlements in northwest China presented a small-scale decentralized distribution pattern; the natural geographical environment (elevation, slope, river, farmland, etc.) had a decisive impact on the distribution of rural settlements in northwest China, and the change of natural environment directly affected the distribution of rural settlements.

By comparison, this paper chose the rural settlements in the metropolitan fringe area as the research object. Through the empirical analysis of Nanjing, it was found that the distribution of rural settlements in the metropolitan fringe area presented a largescale agglomeration distribution pattern, which was mainly affected by economic and social development factors, while the natural environment factors had less impact on the distribution of rural settlements. This conclusion was quite different from the distribution law of rural settlements in northwest China. This difference was mainly attributed to the fact that the metropolitan fringe area was a transitional zone between cities and villages. The rural settlements in the metropolitan fringe area were a concentrated reflection of the human-land relationship, with significant characteristics of rapid economic development and urbanization. Under this influence, the rural settlements in the metropolitan fringe area were facing or experiencing dramatic spatial evolution and modern transformation, and their spatial distribution and evolution patterns were different from those of the rural settlements in other regions.

(2) The spatial distribution of settlements can be used as a basis to show the comprehensive relationship between human activities and the natural environment in a region

and has reference value for the optimization of the spatial pattern of settlements. Based on the analysis of the distribution characteristics and influencing factors of rural settlements, combined with the field research in this typical region, the optimization of the layout of rural settlements in the metropolitan fringe area was attempted to be divided into four types: urban transformation type, key development type, limited development type, and relocation type [70–72].


#### **5. Conclusions**

This paper took the rural settlements in the metropolitan fringe area as the research object, taking Nanjing as a typical case. From three aspects of spatial distribution, scale distribution and form distribution, this paper analyzed the distribution characteristics of rural settlements in the metropolitan fringe area. On this basis, this paper tried to reveal the influencing factors in the distribution of rural settlements in the metropolitan fringe area. The following conclusions were drawn:

(1) The spatial distribution of rural settlements was significant in the metropolitan fringe area, it showed the characteristics of "agglomeration" spatial pattern. The spatial distribution of rural settlements generally presented a "multi-core" center, and a spatial distribution trend of stepwise declined from the core to the periphery, showing a typical "core-edge" structure. The core of rural settlements in the metropolitan fringe was mainly distributed in the agricultural counties in the outer suburbs, while the surrounding villages in the main urban area were radiated by the city, and the population was urbanized locally. Rural settlements gradually evolved into urban settlements, resulting in less spatial distribution of rural settlements.

(2) There were significant differences in the scale distribution of rural settlements in the metropolitan fringe area, showing that the scale of rural settlements gradually decreased with the increase in the distance from the central city. The overall distribution pattern was that the scale of rural settlements in the near suburbs was large, the scale of rural settlements in the outer suburbs was moderate, and the scale of rural settlements in remote areas was small. The closer the rural settlement was to the built-up area, the more affected by human activities and policy factors, the easier it was to form a large-scale rural settlement distribution.

(3) The morphological distribution of rural settlements had good stability in the metropolitan fringe area, and the spatial self-organization of the distribution of rural settlements was strong, which showed that structural factors (topography, geomorphology and other geographical environmental factors) and random factors (economic development, policy system, etc.) jointly played a role in the differentiation of rural settlements in the metropolitan fringe area. The morphology of rural settlements mainly included strip, arcbelt, cluster, scatter types, the formation of different settlement types was closely related to the natural geographical environment, historical and cultural factors.

(4) The distribution of rural settlements in the metropolitan fringe area was mainly affected by topography, river system, traffic, economic development, cultural and policy. Among them, the distribution of rural settlements had the location orientation of "low altitude, close to river and close to road", and the natural geographical environment has laid the foundation for the distribution pattern of rural settlements in the metropolitan fringe area. The increase in agricultural population and the development of rural economy played a leading role in the distribution of rural settlements in the metropolitan fringe area; the cultural and policy factors played an important guiding role in the distribution and reconstruction of rural settlements in the metropolitan fringe area.

**Author Contributions:** Conceptualization, R.Z. and X.Z.; methodology, R.Z.; software, R.Z.; validation, R.Z.; formal analysis, R.Z. and X.Z.; investigation, R.Z.; resources, R.Z.; data curation, R.Z.; writing—original draft preparation, R.Z.; writing—review and editing, R.Z.; visualization, R.Z.; supervision, R.Z.; project administration, R.Z.; funding acquisition, R.Z. All authors have read and agreed to the published version of the manuscript.

**Funding:** This study was financially supported by the National Natural Science Foundation of China (42101201), by the Humanities and Social Sciences Foundation of the Ministry of Education (20YJCZH230), by Research Project of National Agricultural Professional Degree Graduate Education Steering Committee (2021-NYYB-07), by the "High-end Talent Support Program" of Yangzhou University, by the "Qinglan Project" of Yangzhou University.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**

