1. Introduction
Regional traditional villages are widely distributed all over the world. When considering the concept of regional traditional villages, “regional” relates to the limitations of the local geography and local environment [
1], while “traditional” relates to experiences, history and memories [
2]. These two terms support each other. Because of the different regional conditions and traditional history, they have different styles and characteristics. For example, in some regions of Central and South America, houses with wide distances are formed due to fallow land, forming discrete settlements with loose forms [
3]; in Iran, due to the topographic conditions of steep slopes, platform-roof settlements have been formed following the trend of desert [
4]. Although the characteristics of each village and architecture are unique, the overall development process and value cognition process of traditional villages generally follow the common law.
From the perspective of development process, regional traditional villages are often defined as complicated systems that are produced by both spontaneous power and design power [
5]. Spontaneous power occurs in the early stage when there is relatively low productivity. The adaptability of human to the natural environment determined that the development of traditional villages was often passive. The agricultural production mode [
6], the infiltration of life and culture [
7] and the restriction of ecological environment [
8] all determine humanity’s dependence on and pursuit of wind, light, water and land [
9]. It is not until the middle and late stage, where there is relatively mature productivity, that design power is developed. Residents will consciously arrange physical space elements such as houses, roads and farmland according to corresponding functions and forms, forming an adaptive combination [
10]. Spontaneous power and design power together create colourful traditional villages that are in step with different regional elements.
Value cognition process can be considered as a further deepening of the development process. Traditional villages are representative of civilization in the pre-industrial age, and the rapid globalization, urbanization and modernization in recent times have had serious impacts on their protection and heritage. Problems such as cultural homogenization, social hollowing and appearance changes need to be urgently addressed [
11]. Cultural homogenization is produced along with the process of globalization, which makes regional traditions and cultural values more easily threatened by economic forces [
12]. In this trend, a large number of regional cultures are easy to be regarded as symbols of poverty and backwardness, and are confronted by modernity [
13]. Therefore, it has become the universal recognition of the academic circle to cultivate local knowledge creation and make cultural diversity flourish in the world [
14]. The process of urbanization leads to further loss of rural population, resulting in the hollowing out of society [
15]. Some traditional villages are in long-term decline and on the verge of disappearing [
16], and others transformed into a part of the town and completely changed the original form of social existence [
17]. In the modernization process of transforming from agricultural civilization to industrial and information civilization, the mode of production gradually presents a state of half agriculture and half industry [
18]. The original self-sufficient rural production and lifestyle has been basically replaced by market-oriented and commercial urban production and lifestyle. Therefore, traditional villages also lose their own source of power, in which the appearance changes become the most intuitive expression [
19]. Based on the above trend, most countries will inevitably have the conditions to pay attention to historical culture and traditional villages, and adopt a protection system in accordance with their own national conditions when dealing with these problems after the social development has reached a certain stage [
20]. As those countries that began to undergo industrialization and urbanization many years ago, the United Kingdom (UK), the United States (US) and other pioneer countries has considered the value of traditional villages since the 19th Century [
21,
22]. So far, they have gradually established a more mature protection system. However, the process of industrialization and urbanization in China only started in 1950s [
23]. Compared with developed countries such as the US, the UK, Italy and Japan in the same period, China started later [
24] with a lower starting point, and the situation of urban–rural separation was more serious [
25], resulting in a weaker focus on rural areas. However, China has still established relevant protection systems based on the local experiences of pioneer countries in the past two decades. For example, the Notice for Traditional Village Survey Issued by the Ministry of Housing and Urban-Rural Development of China, the Ministry of Culture, the State Bureau of Cultural Relics and the Ministry of Finance states that traditional villages, which are villages that were formed long ago, have abundant traditional resources, and have historical, cultural, scientific, artistic, social and economic values, shall be protected [
26]. This notice provides explicit requirements to maintain historical remains and traditional villages and implements protective measures through positive administrative management.
As a kind of rural cultural heritage, traditional villages are the social and cultural carriers of a region [
27]. The healthy development of traditional villages is not only a spiritual need of local identity and belonging, but also a practical need to improve the quality of life [
28]. The international community generally recognizes the importance of preserving traditional villages, which can activate local economies and enhance cultural identity [
29]. Studies on traditional villages mainly rely on geography, ethnology and architecture. Among them, the study of geography focuses on the relationship between man and land [
30], the study of ethnology focuses on the relationship between man and culture [
31], and the study of architecture focuses on the relationship between man and architectural space [
32]. Together, they promote people’s understanding of traditional villages, that is, traditional villages are the result of interaction between man and nature in a certain time and space background, and constitute an indispensable part of a specific cultural landscape [
33]. The rich environmental styles, complicated functional layouts and unique artistic characteristics of regional traditional villages contain wisdom and inspiration from historical culture, and thus, must be sustainably developed in the future. The characteristics of these villages require further exploration for socio-economic development through effective protection and management [
34,
35].
However, the protection of traditional villages in China is faced with more special challenges in the world. Existing studies show that in European countries with strong heritage protection traditions and rich social capital, a value-oriented and people-oriented approach is adopted in the protection of traditional villages, thus protecting the physical space and cultural characteristics of local communities [
36,
37]. However, in China, due to the lack of social capital, most of the protection and development of traditional villages are government-led selection and transformation [
38]. Even in Huizhou, where the historical and cultural heritage resources are abundant in this study, the means of protection are more likely to obtain financial support from the government through the listing of “historical buildings” or “cultural relics protected buildings” to maintain the daily maintenance needs of the buildings [
39]. The strength and coverage of this type of protection is far behind the speed of physical destruction, which has resulted in a large number of endangered villages and collapsed buildings [
40]. Based on this, scholars have conducted meaningful research on the endangered status of villages and buildings, such as building activation, renovation, and restoration [
41]. However, traditional villages are not static entities. What they present is a superposition state formed in long-term changes. Any transformation in functions and styles may change its evolution process, especially the subjective design will have low applicability to heritage buildings [
42]. Previous studies are more focused on building units, and it is difficult to determine the correlation between building groups, which also makes some important features and problems difficult to be discovered [
43].
To this end, this study focused on spatial sequences at the building and environmental levels. The concept of spatial sequences originates from aesthetics and covers multiple physiological dimensions, including vision, hearing, emotion, etc. [
44]. It describes the summarization process by which humans acquire a series of continuous images of their environment, forming perceptions of the environment [
45]. Although it is widely believed that spatial sequences are ubiquitous, such perceptual cognitions are complicated and diversified, and often accompanied by individual value judgments. Motloch argued that the behaviours of individuals in outdoor spaces involve a continual process of searching for goals [
46]. Three systems, including the structural state of space, movement experiences over time, and thinking and emotional experiences, must be considered in order to capture the diversity of such perceptual cognitions [
47]. As such, the study of spatial sequences is a process of building and understanding the values (e.g., placeness and experiences) of research objects by capturing and extracting multi-dimensional data. Such a research mode has been applied to various practical designs. For example, in the City of London Local Plan, the UK issued policies for the protection of visual and spatial axial sequences related to the historical site centred around Saint Paul’s Cathedral [
48]. Studies and practical assessments of spatial sequences in England and the protection and renewal practices around the central axis of Beijing, China [
49], have high value and significance.
As described above, spatial sequences are complicated systems and changes in their continuity can be manifested on several levels, such as changes in visual perception sequences represented by colours and the light-shadow environment [
50], changes in auditory perception sequences represented by the acoustic environment [
51], changes in somatosensory sequences represented by the wind thermal environment, etc. [
52]. Among them, visual perception is the most important source by which humans perceive external information [
53]. For regional traditional villages, the visual perceptions of humans generally focus on the composition and organizational relationships of material elements, textures and colours. Among them, the building facade is the most obvious material element. Many studies have attempted to quantize building facades, and most have focused on the physical attribute indices and non-physical attribute indices of building facades. At the physical attribute level, some studies have found that indices reflecting rules and symmetry [
54,
55], morphology and colour [
56], and proportion and curvature [
57] of building facades may have common influences on the aesthetic preferences of individuals. At the non-physical attribute level, non-architects may have different preferences for originality, complexity and meaningfulness of building facades as compared to professional architects, due to their different understandings and professional knowledge [
58]. Moreover, the neuroscience field has found that the brain’s reward system is triggered when a beautiful object is perceived, and this prompts an aesthetic judgment process. Although this process is complicated and multi-dimensional, there are several common decisive factors in describing beautiful things [
59,
60,
61]. In this study, key attention was paid to indices of the building facade that reflect physical attributes. This not only avoided perceptual differences due to differences in professional knowledge, but also allowed for the identification of universal quantitative laws in regional traditional villages.
In a previous investigation of the long-term perceptions of Huizhou traditional villages in Southern Anhui Province, China, and the protective renewal practices of traditional villages and famous historical cultural villages, the current research team identified laws that are worthy of further exploration. Specifically, the travelling laws of residents and tourists through streets in traditional villages were studied through space syntax and GPS technology. The results demonstrated that perceptions are influenced by the family settlement area, with a core settlement area typically evident at the entrance to the centre of the village. Such an internal settlement pattern provides strong centre-oriented guidance for perceptions of placeness and related experiences [
62]. Moreover, this sequential perception process appeared to be strongly related to changes in spatial sequences, light-shadow sequences and other sequences. In Huizhou region, influenced by local culture, typical villages have the spatial sequence organization pattern of “Start-Continue–Turn-End” [
63] in
Figure 1. “Start” and “Continue” tend to refer to the village entrance and Shuikou space, a landscape entrance in traditional Chinese culture. “Turn” tends to refer to the street space with multiple turns. “End” tends to point to the spiritual and spatial centre represented by ancestral halls and other high-level buildings. There are hundreds of Huizhou regional villages in this spatial sequence organization pattern which is highly similar [
64]. Therefore, in this study, the laws of building facades in single building units and groups of buildings under the typical centre-oriented guidance (i.e., entrance–street–centre) were explicated based on a case study of typical Huizhou traditional villages.
To sum up, this study considers that traditional villages are faced with a rescue predicament both in the world and in China’s national conditions: limited by fund conditions, taxidermy protection means are not competent for a large amount of heritage protection work; based on the subjective perception and experience of designers, the activation of reconstruction has a greater risk, which may be unable to identify effective information and lead to the wrong direction of the architectural style; there may be potential laws that are difficult to identify qualitatively among building groups, and these laws are likely to cause sequential damage due to changes in building units or spatial elements. A research method of village monitoring and protection that can consider both objectivity and generalization needs to be further sought.
Under the typical and explicit regional constraints of Huizhou, Southern Anhui Province, China, this study addressed the following three research problems based on the physical attributes of building facades in Huizhou traditional villages:
Which potential factors can control and influence the facade composition of building units in Huizhou traditional villages?
How many typical modes are there in the facade composition of building units of Huizhou traditional villages?
How are building units combined and connected in Huizhou traditional villages to form rhythmical building group facades?
It should be noted that different traditional villages should be viewed as different complicated systems. The local natural environment and local people influence the formation of traditional villages. Therefore, this study evaluates the spatial sequences represented by building facades in regional traditional villages through a case study of typical Huizhou traditional villages. First, the cultural heritage value of Huizhou traditional villages, as well as their common laws, are discussed under the explicit regional constraints of Huizhou. Second, this study emphasizes the perception process of spatial sequences, which is often ignored. As a further deepening of the existing quantitative research on village space, this study also attempts to quantify and summarize the rules of building facades in the two levels of unit composition and group organization. Third, by establishing a spatial quantitative monitoring standard, this study offers a novel research perspective and a feasible technical route for future study of the protection and renewal of traditional villages in Huizhou, and even other regions.
In the next section, the study attempts to establish how to obtain the accurate facade information of Hui-style architecture, and how to extract and analyse the information, so that the whole scientific process has the characteristics of rapidity, objectivity, and generalizability. The systematic methodology employed to explore the spatial atmosphere design, centralized common styles, as well as sustainable development and utilization of traditional villages is described.
4. Discussion
This study investigated the typical regional laws of the facade composition of building units and the facade organization of building groups in regional traditional villages. Specifically, building facades in Hongcun, Nanping and Xidi in Southern Anhui Province, China, were investigated. Based on previous results from the research team, facade information acquisition, digital model construction and index selection and calculation were carried out. On this basis, the ability to quantify and statistically analyse building facades at the building unit and building group levels was verified. The findings are described in more detail below.
The facade composition of Chinese Hui-style building units are controlled and influenced by the transparency factor, volume factor and shape factor.
Case studies were carried out using 325 building facades on each side of three spatial sequences in three Huizhou traditional villages. Nine integrity indices and hierarchical indices were input as the original variables in the factor analysis. After the feasibility of factor analysis was confirmed, factors were identified and rotated using PCA. Factor scores were calculated, and three potential factors were determined: a transparency factor, volume factor and shape factor. In previous studies, Hui-style building facades are usually described based on qualitative perceptions as enclosing, introverted, strewn at random or regular [
84,
85]. In this study, the accuracy of the above perceptions was first verified, and was almost identical to the meaning of the three factors. Specifically, the transparency factor reflects the virtual proportions of doors and windows. The volume factor reflects the size of buildings. The shape factor reflects the flexibility or irregularity of building shapes. The construction of the facade was further evaluated by reducing the dimensions of the data. Assisted by the deletion of irrelevant information, this study provides a deeper qualitative and quantitative understanding of the facade composition of Hui-style buildings and explains the controlling and influencing laws of the three potential factors. Previous studies also hold that the remarkable characteristics of Hui-style architecture are closed exterior walls, exquisite doors, window decoration and elegant shape [
86,
87]. These characteristics can be quantified and described by the results of factor scores, which further answers how the facade is formed, and can make the linear equations of these factors closer to a stable value with the increase in future research samples. Therefore, these three potential factors are consistent with the cognition of previous studies and have a certain rationality. It should be noted that it is inevitable to lose information during factor analysis since it is a process of dimension reduction. Although the loss of information is conducive to the extraction of the most important information, the reduced data still has to be compared with the original variables to ensure the accuracy of the results and interpretation, the feasibility of the relevant indices, and the suitability of the data for factor analysis. The process of factor analysis is closely related to the initial indices [
88]. The building facades of traditional villages in different regions may lead to the differences in the initial indices, resulting in the differences of factor analysis. Therefore, the results of factor analysis in this study cannot be directly applied to traditional villages outside Huizhou.
The facade composition of Chinese Hui-style building units can be summarized according to five typical modes: flexible mode, introverted mode, tall mode, extravert mode and enclosing mode.
Based on the above factor analysis, systematic clustering of the scores of the 325 cases for each of the three factors was further carried out, and five typical facade composition modes were extracted: flexible mode, introverted mode, tall mode, extravert mode and enclosing mode. As the facade of Hui-style building is mainly composed of solid building components such as the roof, Ma Tau Wall, doors and windows, the facade form has been highly purified through historical accumulation [
89]. Specifically, flexible buildings are mainly landscape structures and some small buildings with complicated shapes, which reflects the ethereal and tortuous characteristics of Huizhou landscape building [
90]. Introverted buildings are mainly traditional Hui-style building facades and the side walls of some buildings. The side facades of Hui-style residential buildings are mostly closed gables, and the Ma Tau Walls are mostly presented with horizontal lines, which is conducive to the splicing [
91]. Tall buildings are mainly high-class public buildings. Small windows are set on the large wall to form a sharp contrast, thus reducing the oppressive feeling caused by the excessive wall area [
92]. Extravert buildings are mainly business buildings, open residential buildings and gates of courtyards, which reflect the characteristics of the “front shop and the back house” of the business buildings, presenting the open shape of the storefront suitable for trade [
93]. Enclosing buildings are mainly building walls, which reflect the spatial characteristics of deep and serene streets and alleys in Huizhou traditional villages [
94]. On one hand, the cluster analysis quantitatively demonstrated the dynamic influencing processes of the transparency factor, volume factor and shape factor. On the other hand, it provided deeper insights into the facade composition. To explore these five building modes more intuitively, four spatial modes (landscape space, street space, corner space and others) were introduced. The mode distribution diagrams of the three traditional villages were drawn according to their actual, real-life proportions. Although the three traditional villages are independent of one another, the distributions of the building and spatial modes exhibited similar characteristics due to the influences of the regional natural and human environments. This further verifies the reasonability of the above factor analysis and cluster analysis results. It should be highlighted that as a classification process, there are many possible clustering methods and measuring methods that can be used for cluster analysis, all of which have implications for the research. Although the ultimate clustering results are generally consistent, differences in clustering results due to different algorithms cannot be avoided. The clustering and measurement methods used in this study should be considered when interpreting the current results. Meanwhile, the five typical modes are mutually exclusive and consistent with the cognition of previous studies, which are reasonable to a certain extent. However, the data come from the selected samples and cannot cover all the building modes in Huizhou. With the increase in future research samples, the clustering model may be further refined.
In the facade organization of Chinese Hui-style building groups, group combinations and group connections of modes have obvious regional commonalities.
There are no direct overlaps in the planning and construction of the three villages. However, they are all located at the core zone of Hui culture. Influenced by Hui culture and the construction technologies utilised for Hui-style buildings, they exhibited similar laws, which were manifested in group combinations and group connections. With respect to group combinations, the results revealed that the spatial sequences in all villages formed five to seven typical combinations, with an average length of about 70 m. These combinations were formed by a combination of two to three building and spatial modes. Moreover, introverted buildings accounted for the highest proportion in terms of the cumulative length of group combination, while introverted buildings and extravert buildings accounted for the highest proportions in terms of the cumulative number. The main combination types were combinations of building modes dominated by introverted buildings and combinations of building and spatial modes dominated by flexible buildings. Hui-style buildings are an introverted and enclosed composite architecture centred on the courtyard, which is closely related to the implicit features of Hui culture and Chinese traditional culture [
95,
96]. In terms of group connections, the proportion of spatial modes was increased significantly compared to single building units. Landscape space and extravert buildings are the main elements in the facade organization of building groups. It is closely related to the characteristics of traditional business buildings, which are both merchants and houses. For the purpose of management and trade, business buildings open to the outside and circulate inside [
97,
98]. Therefore, it can be concluded that spatial sequences dominated by buildings and supplemented by spaces are typical in Huizhou traditional villages. Spatial sequences are often formed by an organizational mode centred on introverted buildings, and connected with extravert buildings. Such organization laws are influenced by the traditional internal clustering plane of buildings and the introverted culture. There were several additional meaningful findings in the study. From the perspective of regional humanities, the independence of tall buildings reflects the high-class features of these buildings. The high connection intensity of flexible buildings and landscape spaces reflects the positive adaption and reconstruction of Hui-style buildings within the surrounding environment [
99]. The relatively high connection intensity between introverted buildings and corner space might be closely related to the demands of local people for defence against enemies and thieves [
100].
As regional traditional villages have always been in a dynamic development process, not only architectural functions and styles have undergone restoration and changes, but also people’s understanding of architectural information has different understanding due to different knowledge level and value cognition. It is easy to bring inconsistent subjective judgment in the actual protection and updating of historical heritage. Thus, a statistical method based on combination of factor analysis and cluster analysis was discussed from the research perspective and technological route. A technological route composed of 3D laser scanning technology, 3D digital modelling, 3D data vector operation, factor analysis and cluster analysis, and construction of spatial sequences was built. The most core underlying logic of this set of analysis tools is induction. While extracting accurate historical and cultural information that does not depend on people’s subjective judgment, it can still effectively eliminate local variation information and retain most traditional information. The accurate data obtained by this method can be stored as the architectural information database of historical heritage, which can be analysed and discussed at a deeper level in the future. This series of studies have been practiced gradually in Huizhou region. Results provide positive references to activation and protection of traditional villages in Huizhou region and even other regions. For example, through the rapid acquisition of 3D data to repair and rebuild collapsed buildings; in style renovation and design, factor and cluster analysis is used to help architectural planners identify the overall style, retain the original historical and cultural information to the maximum extent. These practices promote the exploration of effective integration of history and modern life.