CLGTS is an important method for establishing CLGTS Tupu in China [32, 36]. CLGTS Tupu means that people employ the principles and methods of Geo-Information Tupu [31] to map and address the core features of CLGTS in a given region. CLGTS Tupu is of great implications to understand the cultural features of traditional settlements of a given region from a geographic perspective. For example, we can use CLGTS Tupu to show the natural features of a certain important cultural factor of a given traditional settlement. It thus is of great significance to clarify the scientific characteristics of CLGTS. In this work, we mainly explore the scientific features of CLGTS from three aspects: dialectical features, morphometric features, and structural features.
The dialectical features
Richard Dawkins first introduced the concept of gene into the socio-cultural areas, and proposed to use it as a “meme” in 1976 [38]. E. O. Wilson presented the theory of co-evolution of human gene and socio-culture based on the genetic characteristics of human socio-cultures [39, 40]. Geographers mainly study the features of regional cultural genes from the perspective of humanism. For example, Conzen proposed the Morphogenesis Theory in 1988 [18].
CLGTS theory has been nourished by ancient Chinese ecological thinking, plan concepts, and the philosophy of man-land relationship [41]. Since its introduction, CLGTS has developed a series of methods to identify the outstanding cultural factors in traditional settlements, such as pattern, text, element, and structural features [33, 42]. CLGTS is of scientific significance since it provides cultural geography with the analysis methods of natural sciences to explore the features of traditional settlements. This is meaningful from the perspective of scientific philosophy.
To begin with, CLGTS is a dialectical combination of a macro image of traditional settlement landscapes and their micro cultural factors. From the conceptual scope of CLGTS, cultural landscape genes are the uniquely identifiable [43]. In practice, people mainly think about the image features of traditional settlement landscapes from a holistic perspective to distinguish different settlements with similar cultural properties. For example, only by treating the three scattered blocks as a whole (Fig. 1) can we understand the dragon-shaped layout of Zhangguying Village [32] in Hunan Province, China. The cultural landscape genes usually hidden in different traditional settlements can reflect the cultural differences of settlements in different details or at different levels. For example, Ma Tau Wall is a common architectural decoration style in traditional Chinese courtyards; however, Ma Tau Walls often have different cultural differences in different regions, which can only be distinguished by details such as shapes, arcs, and bends [44].
Furthermore, CLGTS is a dialectical combination of physical appearance features and inherent traditional cultural meanings of traditional settlement landscapes. The cultural factors of traditional settlement landscapes usually have the corresponding physical carriers. In fact, even the intangible cultural factors of traditional settlements can also reflect the key characteristics of related objects. For example, only by providing a certain space in Chinese traditional settlements can the Nuo Opera be performed, which is one kind of traditional operas originated in some rural areas in China [44]. As long as the following conditions are met, a cultural factor can be truly defined as a recognizable CLGTS: (i) it must undertake the certain special functions conferred by traditional settlements; (ii) it must occupy a specific spatial position in traditional settlements; and (iii) it must reflect some social ethics, functions, or cultural meanings contained in traditional settlements. Note that only meeting the above conditions can a CLGTS be significant when capturing the spatial image of a given traditional settlement.
In addition, CLGTS is a dialectical combination of the entire features and local self-renewal mechanisms in the inheritance process. It is well known that biological genes can maintain their own characteristics in the genetic process without fundamental changes. However, a certain degree of trait changes of biological genes (e.g. mutation) can also be induced or triggered by some peculiar factors. For example, tobacco smoke associated DNA adducts may cause mutations in human larynx squamous cells [45]. The same is true of CLGTS in the process of inheritance. Cultural landscape genes always try to maintain the stability of their important features or attributes. On the other hand, due to different cultural ecological environment, the cultural landscape genes will also undergo corresponding changes in the process of their spread. This implies that a certain degree of self-renewal has emerged in some details. For example, for the Hakka Tulou, although their enclosure patterns have changed from square to quasi-square and then circular, their main features are still kept, such as function, social statute, and cultural meanings [46].
Additionally, CLGTS is a dialectical combination of qualitative and quantitative analysis methods of traditional settlement landscapes. In the history of geography, qualitative methods have long been the mainstream research methods. Since the revolution of computation geography [47], quantitative methods have gradually become popular. However, in the domains of cultural geography, scholars tend to employ qualitative methods when tackling with research issues. We notice that CLGTS has organically combined qualitative and quantitative methods by introducing some bio-informatic methods. This will help to enrich the methodologies of cultural geography. For example, the exploration of CLGTS spatial patterns of Hunan Province, China mainly used qualitative methods [34]; however, the exploration of CLGTS genome maps of Hunan Province, China mainly used quantitative methods [33].
Finally, CLGTS is a dialectical combination of the superiority of core features and the cultural connotations of traditional settlement landscapes. In the traditional settlement landscapes, CLGTS is one of the most recognizable cultural factors. For example, Gulou is the grandest and the most majestic building in the Dong Minority villages/camps, and vice versa: Gulou is also the most important cultural symbol to identify the Dong Minority villages/camps. CLGTS usually contains rich cultural connotations. This means that CLGTS can reflect many important features of traditional settlements. What needs to be emphasized is that although the superiority of core features and cultural connotations are the two aspects of CLGTS, they are consistent, not opposite.
Through the above dialectical relationships, we can conclude that CLGTS is a scientific concept (Fig. 1). CLGTS is not only an objective reality but also contains profound and rich traditional cultural characteristics, such as traditional social institution, traditional ethic, traditional philosophy, traditional custom, and clans, etc. In addition, CLGTS can not only explore the scientific features of traditional settlement landscapes from the perspective of natural science, but also generalize the cultural features of traditional settlement landscapes from the perspective of cultural geography.
Morphometric features
CLGTS has its own physical characteristics and appearances. And in the traditional settlement space, CLGTS is full of close connections, rather than isolated. For example, the Dang Gate of Zhangguying Village (situated in Yueyang County, Hunan Province, China) consists of a group of Chinese traditional courtyards [48] arranged on the same axis of symmetry, and its entire spatial layout is designed as a Chinese character “丰”.
In the process of site selection, design, and construction, many Chinese traditional settlements have emphasized the need to maintain the traditional customs and show their own characteristics. They also pay attention to creating spatial image with rich traditional cultural meanings according to different geo-environments, time, places, and landscapes [49]. In ancient China, people usually tended to create a spatial layout with rich geomancy beliefs [50] in terms of the corresponding natural environment while constructing the settlements. For example, the Longjia Courtyard Group of Heizuling Village (situated in Xingtian County, Hunan Province, China) is famous for its spatial layout of “five generations living together” (According to the meanings of traditional Chinese cultures, this spatial layout means that five generations of the same clan live in the same courtyard together and share the same hall. It hints that a large group of traditional courtyards have been built to accommodate an enormous family.). This objectively contributes to the diversity of CLGTS spatial forms. For example, Z Hu et al. [33] pointed out that the spatial layouts of traditional settlements in Hunan Province mainly include sector and circle.
According to PL Liu et al. [51], CLGTS spatial forms mainly include square series and circular series, as well as various geomantic forms based on environmental conditions (Fig. 2). The square series includes different variations based on the square shape. For example, many spatial forms are derived from the courtyard dwellings/Siheyuan, such as Jing/yard, Hall, and patio/Tianjing [48]. The circular series includes a couple of variations based on the circular shape, mainly including ellipse and quasi-circle. For example, the spatial forms of Tulou in Fujian Province [50] mainly include circle and ellipse. To sum up, the spatial forms of Chinese traditional settlements have changed from square to circle, and then to irregular shapes [51].
It is important to stress that, in ancient China, the northern region is the main habitat for people. In north China, the relief is low and the main landform is plain. In ancient China, people often designed and constructed regular square houses, courtyards, and settlements. Because the traditional geomancy originated thousands of years ago in ancient China highlights ‘Heaven was round’ and ‘Earth was square’, and the traditional geomancy dedicated to enhancing and maintaining the co-existing relationships between human beings and natural environments. In ancient China, people had been pursuing the harmony survival with nature. And this has been the main aim of geomancy from ancient to now. In history, the spatial form of house and settlements had turned into circle when people migrated from north to south due to the lack of plains in south China.
Structural features
CLGTS shows different characteristics in spatial organization and forms various spatial structures with rich traditional cultural meanings [33]. With reference to the existing research cases [33, 46, 51], it can be found that the spatial structures of CLGTS have the characteristics of nonlinearity, self-organization, and self-iteration.
First, CLGTS is nonlinearly arranged in the traditional settlement spaces. As we all know, for physical space in nature, the linear spatial structure is a common arrangement, which can be accurately described by linear equations. The constituent elements of traditional settlements are nonlinearly arranged, which is determined by the natural geo-environment conditions in which the traditional settlements are located. The natural geo-environment is full of complexities, nonlinearities, and randomness. This makes it difficult for different constituent elements in traditional settlement spaces to form a regular linear arrangement, such as streets, and alleys.
In fact, the layout of the constituent elements of traditional settlements must be in accordance with the geo-space where the settlements are located. The constituent elements of traditional settlements thus are difficult to be regularly arranged like the linear structures, because their arrangement is mainly affected by the geo-environments. At the same time, the arrangement and layout of the constituent elements of traditional settlements are also planned according to the design ideas and concepts of settlements in ancient times. To a certain extent, CLGTS can be understood as the mapping of various cultural factors in the traditional settlement space on the socio-cultural dimensions. This suggests that the cultural factors or non-material cultural factors in the traditional settlement space are also nonlinearly arranged. For example, the most ideal city in ancient China recorded in “Kao-Gong-Ji”Footnote 2 is a 3-Li (an ancient length unit in China) square city; however, due to the complexity of the geo-environments, it is difficult to construct an ideal city with ideal spatial layouts in the real world.
Second, CLGTS shows the self-organizing features in traditional settlement space. We know that the size of a settlement will expand in the process of its development as the population grows. All the constituent elements of settlements gradually change from irregular to regular and from disorder to order. This is not only in accordance with the evolution law of natural systems, but also in accordance with the development process of human civilization. In fact, the constituent elements of traditional settlements are organized well and are not in a mess. Through organic planning of various constituent elements, many traditional settlements created spatial structures with special cultural significance. For example, Zhuge Ancient Village (located in Zhuji City, Zhejiang Province, China) is famous for “Eight-Diagram-Street-Alley” spatial structures [52].
In addition, the constituent elements of settlements with similar functions also tend to congregate together. Because the congregated constituent elements (e.g. shops/stores) can ultimately share the common infrastructures of settlements and attract customers. For example, the intact Water-StreetFootnote 3 can still be found in the ancient towns south of the Yangtze River in China, such as Zhouzhuang Ancient Town [53], Tongli Ancient Town.
Third, CLGTS also has the characteristics of self-iteration in the traditional settlement space. Iteration is a regular self-similarity that can be accurately described by mathematics. In nature, the objective objects with iterative characterizations have precise spatial structures, such as honeycomb, tree texture, biological genes. In fact, many precise spatial structures can also be observed in CLGTS. For example, ancient buildings in traditional settlements often use patterns or textures with precise structures to decorate windows. Iteration can also be considered as a self-repair and self-development mechanism of natural systems during the evolution process. In fact, the self-iteration phenomena can also be found in the humanities and society. For example, the generation reproduction of families is a regular iterative process that can be recorded by genealogy [54].
The self-iterative features of CLGTS are similar to biological genes. Because the cultural connotation, appearance characteristics, and physical carriers of CLGTS are completely replicated and spread during the inheritance process. For example, in the field investigations in Jingshan Ancient Village (located in Rucheng County, Hunan Province, China), Z Hu et al. [55] found that the techniques and experience of making Hong-Meng-Liang,Footnote 4 which originated hundreds of years ago, were completely inherited by the craftsmen of this village.