Juxtaposition or integration: the formation mechanism of architectural form in a cultural transition zone

ABSTRACT This paper explores the formation mechanisms of various architectural forms in a cultural transition region. A field investigation involving 504 ancestral shrines with Guangfu and Hakka styles in Shenzhen was performed. Then, spatial distribution analysis was conducted to reveal the regional structure of aggregation, penetration and juxtaposition of the architectural forms. Case studies were adopted to explain the integration modes of the architectural forms. The results show that, juxtaposition, as a typical mode of coexistence of architectural forms in cultural transition zones, mainly occurs in regions dominated by weak cultures. Through gathering densely in a small region, a weak culture can gain the ability to compete with a strong culture, thus forming a basis for achieving an equilibrium state. The approaches to the integration of architectural forms are diverse. The transformation of the architectural plane involves changes in social organization and cultural essence. The alteration of construction details and decoration involves a compromise regarding noncritical elements adopted by the weak culture to maintain its original characteristics. Finally, their shared human and natural environmental “genes” give the buildings in the cultural transition region an underlying commonality. This study offers a significant addition to the cultural geography and architectural morphology literature.


Introduction
The relationship between culture and architectural morphology has been extensively discussed. It is generally accepted that different cultural characteristics are key in shaping various building forms (Amos, 1969, Bernard, 1987. The philosophies, concepts and technologies of building construction can be regarded as the results of the influence of culture to a large extent (Amos, 1990, Emmons, Lomholt, andHendrix 2012). In addition, cultural geography theory indicates that in terms of spatial distribution, culture follows a core-periphery structure (Champion 2005;Rowlands, Larsen, and Kristiansen 1987). The core area represents the main cultural features of the whole region. In the periphery, transition areas between cultures emerge due to the homogeneity of culture weakening as the distance from the core increases (Sauer 2008;Jordan, 1986). As a phenomenon and process of culture, the physical form of architecture also follows a core-periphery pattern (Ronald, 1986). Compared with those in the core area, buildings in a transition zone are influenced simultaneously by different cultures. This will inevitably increase the complexity of the formation mechanism of the architectural form.
Shenzhen is a large city on the southern coast of China. Historically, it has been dominated by the dual Guangfu and Hakka cultures, thus characterizing it as a cultural transition region ( Figure 1). Most of its ancient buildings have been demolished, but the ancestral shrines, under the protection of the clans, have been retained. They have become precious cultural heritage sites in this modern city. During the field investigation, we found that some ancestral shrines in Shenzhen have undergone obvious changes in their physical forms, which are presented in a variety of ways. Thus, these shrines serve as appropriate objects to study the architectural forms in a cultural transition zone. Therefore, this study analyses the features and distributions of the built form of the ancestral shrine in Shenzhen by collecting a larger set of samples to provide verification materials and solid empirical support for the existing research. At the same time, the formation mechanism of the heterogeneity and homogeneity of built form of the ancestral shrine is explained through the pattern of spatial distribution, which may bring new insights to the scholarly discussion of architectural morphology.

Ancestral shrine and its cultural connotation
The ancestral shrine or family temple, as an important symbol of clan culture under the Confucian belief system, was a type of sacrificial and commemorative building in ancient China. In contrast to temples and churches, they were not only where blood-related family members worshipped ancestors and sages but were also gathering places for marriages, funerals, longevity celebrations and deliberation regarding important clan affairs (Wu, 2010;Liu 2003;Jin 2018).
Studies have shown that the design and construction of ancestral shrines were essentially influenced by traditional Confucian culture (David and Liu, 2000). First, the classic Confucian book "Family Ritual", which was written in the Southern Song Dynasty, laid the basic rules for the spatial pattern of ancestral shrines for later generations (Zhu 2002). Thus, the prototype, namely, the front gatehouse as a prelude, the grand middle hall for worship, and the ending hall for ranking the tablet of ancestors, was inherited (Feng 2017). Second, traditional sacrifice etiquettes had an impact on the setting of the ritual space. The sequence of construction, arrangement of rooms, indoor furnishings, and placement of altars and ancestral tablets were all controlled by the sacrificial regulations (Gong and Guo 2008). Third, the ethical order emphasized by Confucianism was reflected in the built form of ancestral shrines. According to Feng's (2017) research, the setting of steps, doors, gable walls and so on were all related to the identities of the space users; they were used to distinguish the hosts and guests, men and women, and the generations of people. In addition, the social function would also influence the shrine's built form. For example, to better civilize the clan people and convey Confucian ethics, the gatehouse of the ancestral shrine always adopted the form of an academy building.
That is, open spaces were set on both sides of the gate, inside and outside the wall (Zhong 2018).
As a mapping of Confucian clan culture, the ancestral shrine exhibited some internal commonalities. However, to better suit the specific natural and cultural environments in different regions, adaptive design could always be observed. Thus, the ancestral shrines show certain regional differences (Yang 2008). Therefore, based on the homogeneity of the general spatial form, partial and diversified variation constituted a basic logic for understanding the built forms of ancestral shrines. This is an issue that deserves scholarly attention and will be discussed in the following section.

Cultural confrontation and architectural forms
The phenomenon and mechanism of culture shaping architecture have been reported worldwide. This is seen, for example, in the influence of Islamic religious customs on mosque architecture (Hisham, 2003, Mohammed Abdullah Eben, 1998, the impact of social cultural patterns on domestic building spaces in the Mediterranean region (Paul, 2000), and the effect of etiquette systems on traditional Chinese architectural morphologies (Steinhardt 2019). This paradigm of research aims to reveal the mapping between a single culture and a building form, and the samples are located mainly in cultural core areas.
Specifically, under the influence of colonial culture, colonial architecture represents different physical features from the native architecture, as seen in Britishstyle houses in the United States (Hugh, 1987), Spanish-style houses in Mexico (James, 1994), and French-style houses in Algeria (Joëlle, 1996). Although such scenarios involve two cultures, they are not spatially adjacent, and there is no cultural transition area. However, the phenomenon in which a strong colonial culture integrates with the local culture is observed. After analysing the French colonial architecture in Laos, (Xayaphone, 2015) argued that the colonial culture changed rather than eliminated the local culture, and the combination of the two building forms was better suited to the local religion and climate. Demissie (2012) examined the Italian colonial architecture in Libya and pointed out that the mixture of local and imported architectural vocabulary shaped a new architectural form called "Libyan rationalism".
When cultures came into contact and confronted each other in the cultural transition zone, they would adjust and adapt, thereby developing new architectural forms (Li, 2009). In this process, two types of architectural form transformations were observed, namely, linear gradual inheritance and parallel mutation (Li et al. 2020). In addition, the integration of architectural forms caused by cultural fusion needed a specific basis, that is, a certain potential difference between the two cultures. This potential difference should occur under the circumstances that the strong culture could affect but not fully assimilate the weak culture (Peng et al. 2016). Kellner-Heinkele, Gierlichs, and Heuer (2008) introduced the architectural characteristics of Crimea, the Caucasus, and the Volga-Ural regions on the edge of Europe, where different building styles represent a state of juxtaposition, reflecting the cultural heterogeneity of the areas. Emma Maglio studied the architecture and urban forms on the Aegean island of Rhodes influenced by Ottoman culture and found that the strategy adopted by the strong Ottoman culture was to make full use of the existing buildings and transform their functions gradually to encourage residents to adapt to a new residential culture (Maglio 2012). This case provides another possible process of cultural confrontation, that is, a gentle and gradual transformation based on respect for the built environment.
The above analysis shows that there are diverse modes of response modes to confrontations between two cultures. Sometimes the responses are characterized by rigidity, and architectural forms juxtapose; sometimes they present elasticity, and architectural forms merge. In other cases, the built environment gradually changes, and cultures adapt. These mechanisms of cultural interlacing can also be found in Shenzhen, of which the ancestral shrines are solid evidence.

Materials and methods
Beginning in 2018, a field survey of ancient buildings and ancestral shrines in Shenzhen was conducted by the research team. A total of 504 samples were collected, including 296 Guangfu ancestral shrines and 208 Hakka ancestral shrines distributed in 51 subdistrict units. To conduct a comparative study, we recorded the differential features of the key elements of the two types of ancestral shrines, including the pattern of the shrine-dwelling relationship, the architectural plane, the building materials, and the construction details and decorations.
Then, a research method combining spatial distribution analysis and typical case analysis was adopted. The collected samples were spatially positioned, highresolution remote sensing images; the boundaries of subdistrict units were superimposed on the images, and the features of the samples were individually labelled. On this basis, on the one hand, the spatial distribution patterns of the key features were analysed, based on which the structure of the agglomeration, penetration and juxtaposition of the architectural form was explored. On the other hand, through the morphological analysis of the typical ancestral shrines, the approaches of cultural interlacing were explained in an intuitive way, providing micro evidence supporting the macro spatial analysis, as the purpose was to reveal the diversified generation mechanism of architectural forms in the cultural transition zone.

Types and features of the ancestral shrines in Shenzhen
There are two types of ancestral shrines in Shenzhen, namely, Guangfu and Hakka shrines. Guangfu is an important ethnic group in southern China. With Cantonese as its mother tongue, it takes Guangzhou in the Pearl River Delta as the cultural centre and radiates outward. The western part of Shenzhen is an area dominated by Guangfu culture. The Hakka are an ethnic group distributed in the area where the provinces of Guangdong, Fujian and Jiangxi meet in South China. They are immigrants of Han nationality who have historically been displaced by war (Leong, Wright, and Skinner 1997). They are distributed along the Dongjiang River to the eastern part of Shenzhen. The Hakka people retain many ancient cultural characteristics of Central China, and their architectural style is very different from that of the Guangfu (Constable 2005). A detailed comparison of the Guangfu and Hakka ancestral shrines is provided in Figure 2.
In terms of the shrine-dwelling relationship, Guangfu ancestral shrines are built independently in villages, separated from the surrounding small courtyard dwellings (Chen 2012;Lai 2010). In some larger villages, several ancestral shrines of different sizes are distributed at the forefront of dense alley building clusters according to the spatial hierarchy. The Hakka ancestral shrine, in contrast, is integrated into the dwellings as a component (Lai and Yang 2008). Strictly speaking, there is it has no independent architectural form. Hakka dwellings are typically large buildings, and almost all Hakka dwellings have ancestral shrines inside them. This is a key difference between the two types of ancestral shrines.
In terms of the architectural plane, a Guangfu ancestral shrine is generally organized in accordance with the local formula of "Jian", "Jin" and "Lu" 1 (Yang 2013). Importantly, the width of the main building of a Guangfu ancestral shrine is often 3 Jian or 5 Jian, with no wall facing the courtyard. This makes the inner space of a Guangfu ancestral shrine relatively open. Hakka ancestral shrines are neatly arranged along the central axis of a dwelling. They usually occupy a width of only 1Jian, which runs from front to back and is enclosed by solid walls on both sides. It is narrow, closed and has a strong sense of depth. In the case of larger Hakka dwellings, tall and enclosed structures are built on the periphery for safety. This structure will further extend the central axis to a tower called the "dragon hall". It is another part of the sacred space and is unique to Hakka architecture (Pan et al. 2013).
With respect to building materials and decorations, blue brick and wood are commonly adopted for Guangfu ancestral shrines (Xu 2019). Wood is used for the framework of the structure that bears the weight of the building, whereas the walls built of blue bricks constitute an envelope. Red sandstone is also used for the base of the building, door and window frames and columns. In addition, Guangfu ancestral shrines are richly decorated by brick carvings, stone carvings, wood carvings, colourful paintings, grey sculptures and so on (Zhang et al. 2018), which show high artistic skill. Hakka ancestral shrines use raw earth, granite and wood as the main building materials. The earthen wall not only plays an enveloping role but is actually a load-bearing structure because the wooden frame of the roof is built directly on it. In addition, the decoration of Hakka ancestral shrines is not rich, and the appearance of these buildings is simple. The most decorated parts are the altars and niches.
The architectural differences between the two types of ancestral shrines were, to a large extent, determined by the attributes of the commercial culture and agricultural culture corresponding to the Guangfu and Hakka ethnic groups (Guo 2013). Historically, the Guangfu ethnic group lived in coastal plain areas and developed a prosperous commercial culture. To reduce the clan contradiction caused by commercial wealth sharing, individual families played an important role in the social structure of the clan. The family was the smallest unit for economic activities. Therefore, Guangfu village was composed of small courtyard houses. In this case, an ancestral shrine could not be integrated with a dwelling; thus, it was usually built independently (Lai 2010). While the Hakka was a typical agricultural society, collective farming was important for clan self-sufficiency and development. Therefore, in Hakka culture, the concept of individual families was weakened, and the clan branches played an important role. Therefore, the Hakka villages were composed of large dwellings, and a building actually corresponded to a clan branch rather than a family. In this situation, the ancestral shrine would be integrated into the dwellings and used by the branch residents, which was compatible with its social structure (Lin 1997). At the same time, the ancestral shrine was an embodiment of the economic power of the clan in commercial culture. Building a larger and more beautiful ancestral shrine could endorse its business behaviour and enhance the trust of trading partners. Therefore, Guangfu ancestral shrines were grander and more open in spatial pattern. They had more rooms and expanded to both sides, and fine decoration and carvings were usually abundant in different parts of the building. The huge wealth brought by commerce could exactly support this construction (Lai and Yang 2008). In Hakka farming culture, equality was the basis for social stability. The construction of ancestral shrines should not destroy the balance of clans by flaunting individual wealth, so they often showed a more introverted characteristic. As immigrants, Hakka people built walled dwellings for defence. This might limit the expansion of the building and result in a more compact and closed layout of the ancestral shrine (Yang 2011). In addition, the wealth accumulated through farming was limited, which might also restrict the application of luxury materials and decorations in Hakka ancestral shrines to a certain extent. Geographically, the regional centre of Guangfu culture, Guangzhou, flanks Shenzhen to the west, strongly The shrine-dwelling relationship is an important indicator for identifying the cultural type of the village, which reflects the social organization pattern of the community. The pattern of the architectural plane is a core indicator for identifying building types and reflects the cultural traditions associated with the function of the building and family organization. Building materials are an important distinguishing factor. The use of different materials leads to various construction techniques, creating differences between local buildings and buildings in other regions. The construction details and decorations reflect unified cultural features at the regional level and aesthetic taste at the individual level.

Agglomeration and the formation of the transition zone
facilitating cultural radiation. Therefore, the Guangfu ancestral shrines have formed a strong agglomeration core in the western coastal area, with an aggregation intensity that weakens gradually from west to east. It is common for the Guangfu culture to penetrate into the Hakka zone, and Guangfu ancestral shrines are distributed even in the core area of the Hakka zone. While Hakka is an immigrant culture, Shenzhen is located at the end of its diffusion route and is relatively weak in cultural potential. Hence, three smaller agglomeration cores in the east can be observed. Their radiation capacity is weak, the attenuation of the agglomeration areas is obvious, and their infiltration into the Guangfu area is rare.
Accordingly, a delicate spatial equilibrium has arisen. On the one hand, the two types of ancestral shrines have built up stable cultural positions by occupying certain areas in western and eastern Shenzhen and by forming agglomeration cores. On the other hand, by gathering in smaller, scattered areas at a high intensity, the Hakka ancestral shrines are able to compete with the strong Guangfu culture; in this way, the destructive power of penetration by the opponent is resisted, and the cultural characteristics of the ethnic group are maintained.
Abstracted into an illustration (Figure 4), the attenuation curves of the Guangfu ancestral shrines (A) and Hakka ancestral shrines (B) cross, and curve A extends into the high-intensity area of curve B. The attenuation rate of curve A is low, so the slope is relatively gentle, while the attenuation degree of curve B is high. When the two reach a certain balance in potential energy, a cultural transition area is formed.

The interlacing pattern of the architectural forms in the cultural transition zone
In the cultural transition area in Shenzhen, the logic of the architectural form generation is diverse. There is not only juxtaposition but also integration. In terms of the larger human and environmental background, there is homogeneity.

The pattern of juxtaposition
Juxtaposition refers to the non-mutually exclusive coexistence of things in a medium. The juxtaposition of the Guangfu and Hakka ancestral shrines means that the two architectural types coexist in one area and maintain their own features. Taking the subdistrict as the basic geographical unit, we marked those where the architectural forms coexist. The dark grey area in Figure 5 shows the juxtaposition region of the Guangfu and Hakka ancestral shrines, which encompasses 14 units covering a large area of central and eastern Shenzhen. To a certain extent, it shows that juxtaposition is an important pattern of cultural interlacing in the transition zone. Figure 6 shows examples of the juxtaposition of Guangfu and Hakka ancestral shrines. Regarding the spatial distribution, the juxtaposition areas of the two types of ancestral shrines coincide mainly with core Hakka rather than core Guangfu areas. This is further evidence of the cultural penetration pattern proposed above. The circles in Figure 5 show the proportions of the two types of ancestral shrines in the subdistrict units. In summary, there are 67 Guangfu ancestral shrines and 177 Hakka ancestral shrines. The ratio of the two within each boundary is 1:2.6 on average, with a minimum ratio of 1:15. This indicates that although the strong culture permeates the area of the weak culture, the strength of such penetration is relatively low. We can imagine that once the penetration power increases, it might significantly impact the core of the weak culture, which may lead to the collapse of the latter. Spatially, the balance would break, and the weak culture would withdraw. Therefore, the strong agglomeration of the weak culture and the weak penetration of the strong culture constitute a precondition for the juxtaposition in the cultural transition zone to a large extent. In this   situation, the two types of ancestral shrines coexist harmoniously with their own intact characteristics, so there is no new architectural form generated.

The pattern of integration
Cultural integration refers to the merging of adjusted cultural elements to create new systems in the process of cultural exchange and collision. In Shenzhen, the long-term intermingling of the Guangfu and Hakka ethnic groups has resulted in the integration of their cultures. Therefore, new architectural forms of ancestral shrines have emerged.
(1) The shift in the dwelling-shrine relationship: In the Guangfu-Hakka transition area, there is a special village pattern called the "row-house" village, whose main residents are Hakka people. This type of village follows the main structure of Hakka dwellings, namely, row houses, while incorporating the dense alley layout of Guangfu villages. It can be regarded as an integration of the two patterns ( Figure 7). In this type of village, the spatial structure in which the ancestral shrines were originally integrated into Hakka dwellings disappeared, but the need for a space for worship continued. The construction of independent ancestral shrines became a necessity, but there was no corresponding experience in the Hakka tradition. Therefore, imitating the Guangfu was an effective method. We can observe that independent Guangfu ancestral shrines were built in many row-house villages (Figure 7). This combination pattern of Hakka village and Guangfu ancestral shrine is unique to the cultural transition area in Shenzhen.
(2) Collage of Hakka dwellings and Guangfu ancestral shrines: Under these circumstances, the Hakka ancestral shrine on the central axis of the dwelling was directly replaced by the Guangfu ancestral shrine. The Guangfu architectural plane, structure, materials and details were completely adopted. In a very rigid way, the shrines were implanted among the Hakka dwellings, which led to a dramatic visual and cultural mismatch. The Chen family's ancestral shrine, a typical Hakka dwelling in Laoken village, is taken as an example; it adopts a classic Guangfu style, with 3 Jian and 3 Jin. It was built tall and magnificent, and the overall height is much higher than that of the row houses on both sides (Figure 8). This is significantly different from the simple and restrained temperament of Hakka buildings. This collage pattern reflects that the borrowed physical form of the Guangfu ancestral shrine has not yet found an appropriate way to incorporate into the original Hakka dwellings. This may represent an intermediate stage in the transformation of the large Hakka dwellings into the rowhouse villages mentioned above.
(1) Transformation of the hierarchical configuration of Hakka ancestral shrines: The Hakka ancestral shrine is integrated into the central axis of the building; thus, there is usually only one ancestral shrine inside a dwelling. However, during the investigation, we found cases of multiple ancestral shrines inside a typical Hakka residential building. For example, in Qingpai House located in Pingshan District, there are three ancestral shrines facing the front yard and arranged side by side, which is consistent with the layout of Guangfu ancestral shrines in front of a square. According to the interpretation of the aborigines, the shrine on the central axis is the main shrine and the sacrificial space for the whole ethnic group. The other shrines on both sides are branch shrines and memorial halls, and they occupy a lower position in the hierarchy. (Figure 9) An ancestral shrine is the embodiment of the organization of the clan. The adoption of the Guangfu ancestral shrine hierarchy in Hakka dwellings indicates that the Hakka people living there have been influenced by and have assimilated into Guangfu culture. Therefore, the integration is no longer a simple juxtaposition but a deeper fusion. However, the architectural plane adopted by these ancestral shrines still follows the traditional Hakka style. This may be a necessary choice that allows them to be better integrated into the structure of traditional Hakka dwellings.
(4) Details and decorations of Guangfu ancestral shrines used in Hakka ancestral shrines: As mentioned above, under the influence of commercial culture, the Guangfu ancestral shrine adopted more details and decorations, while the Hakka ancestral shrines were plain, reflecting agricultural culture. However, the survey results showed that in the cultural transition area of Shenzhen, the architectural details   and decorations of some Hakka Ancestral shrines also became rich. They often adopted the decoration styles that used to appear only in Guangfu ancestral shrines, and this might happen extensively on different parts of the buildings, such as roofs, doors, windows, and gables. (Figure 10) This phenomenon is common in Shenzhen, and only some typical examples are listed. It is clear that, to a certain extent, the construction details, especially some independent decorative elements, have high flexibility in the process of cultural integration. Technically, they can be integrated into the new building conveniently without changing the cultural attributes of the original building. Notably, most of the changes in construction detail and decoration occurred in the Hakka ancestral shrines. This indicates that in the process of cultural integration, a weak culture is more susceptible to being influenced by a strong culture. Therefore, a weak culture may achieve consistency with a strong culture through adaptive changes in some noncritical elements. This is done to better integrate into the strong culture while ensuring that the essence of the weak culture remains unchanged.

Common genes
The above analysis focuses on the heterogeneous features of the two types of ancestral shrines, as well as their distribution patterns and the mechanisms of cultural interlacing. However, during the investigation, we found that there are also some common features between them. These can be understood as broader aspects of the cultural background and natural environment.
(1) The common cultural genes of Han nationality: Although Guangfu and Hakka are two different cultures, they are both rooted in the Han ethnic group and are two subcultures under the influence of Confucian culture. The same cultural genes shaped some common essential features of their architectural forms, which are reflected in many aspects of the two types of ancestral shrines. However, the most fundamental element of homogeneity lies in the plane pattern.
Chinese Han traditional architecture, whether official or folk, adopts a unified spatial model, that is, the combination of axial symmetrical spatial sequences and multiple courtyards. It has been explained in many studies that this spatial pattern was consolidated over a long span of time and is the physical embodiment of the norms of the etiquette system promoted under Chinese imperial rule (Wang 2006). On the one hand, the core of the etiquette system is to pursue harmony, that is, the balance between different elements, and axial symmetry is considered to be the best and most direct way to achieve this goal. The ancestral shrine, as a spiritual space for clan members to worship, is a direct reflection of the norms of etiquette. Therefore, both Guangfu and Hakka ancestral shrines adopt a strict axisymmetric layout to respond to this basic social criterion. At the same time, the axis strengthens the depth of the building. The ancestors' hall is located in the last Jin of the shrine, and the altar is placed at the end of the central axis, through which the implication of spiritual impact is acquired. Under this setting, the rest of the space on the axis, especially the middle hall used to discuss clan public affairs, was placed under the gaze of the ancestors, which greatly strengthened people's sense of awe in the space. (Figure 11) Figure 11. Similar plane patterns adopted by Guangfu and Hakka ancestral shrines.
On the other hand, another core feature of the norms of etiquette is the implementation of a strict hierarchical system, which creates a fixed spatial hierarchical sequence for the functional layout of the buildings (Li 1993). Only the memorial tablet of ancestors can be arranged inside the shrine; living people are spatially ranked according to generations. The living space of the elders is closest to the ancestral hall; the areas for children and grandchildren expand outward and backwards, and other families are arranged furthest from the ancestral hall. From the sacrificeliving space of Guangfu and Hakka ancestral shrines, we can consistently observe the mapping relationship between spatial order and hierarchy. At the same time, the division between hierarchies of space is realized through the setting of multiple courtyards. When the architecture scale expands, buildings and courtyards appear alternately, forming a natural differential pattern centred on the ancestral shrines. Generally, as the material carrier of sacrificial activities, Guangfu and Hakka ancestral shrines are affected by the same culture gene and reflect a relatively consistent spatial order in the plane pattern. (Figure 11) (2) Common natural environmental genes: In a single area, ethnic groups with different cultural backgrounds face the same natural environment, which means that the settlements and dwellings they live in need to respond to the same environmental adaptability issues. The climate in Shenzhen is hot, humid, and rainy, and it is often affected by tropical cyclones in summer and autumn. Disasters due to rainstorms are severe. In this environment, many climateadaptive design concepts and technologies have been created. These were gradually integrated into the construction designs during the diffusion of the Guangfu and Hakka cultures. As a result, some common architectural forms that reflect wind-proof, drainage and moisture-proof technologies are displayed in both types of ancestral shrines.
First, tropical cyclones with strong winds often cause disasters. For buildings, the roof is a weak link and a key part in wind protection. Its different components, such as ridges and cornices, need special structural designs to resist strong wind. For example, heightened ridges, double-layer tiles and mortar bonding junctions are adopted by both shrines to enhance the weight and integrity of the roof and make it typhoon resistant. In addition, cornice protection forms, such as covering the cornice with gable, setting a cornice board or compacting the cornice with a brick ridge or stone strip to prevent the roof from being lifted by cyclones, are common in both types of ancestral shrines (Tao et al. 2022). These windproof technologies used in ancestral shrines do not exist in the inland Guangfu and Hakka areas far from the coastline (Figure 12(b)).
Second, tropical cyclones are often accompanied by violent rainfall. Quickly discharging rainwater is an important factor that needs to be considered in the architectural design. Because both Guangfu and Hakka ancestral shrines adopt a layout with multiple courtyards, the ground of the building site is designed to be low in the front and high in the rear. By gravity, rainwater flows into the courtyards along the sloping roofs and drains into the pond in front of the village through pipes buried under the buildings and the front square (Tao et al. 2022). Outside the ancestral shrine, rapid rainwater discharge is realized through organized drainage ditches running parallel to the roadways (Guangfu) or corridors (Hakka). Therefore, from the perspective of the drainage system and mechanism, Guangfu and Hakka ancestral shrines are also similar (Figure 12(a)).
Third, the humid climate makes the wood of the building more prone to corrosion; therefore, special moisture-proof treatment is needed. Identical technologies and materials, such as sand and lime, are laid down in multiple layers to build a raised foundation to prevent underground moisture from rising to the floor through capillary action. Fired large bricks with a fine porous structure cover the floor to prevent the water from condensing on the floor and to keep the floor dry. In addition, the indoor columns are made of stone bases and wooden bodies, while the outdoor columns are made completely of stone, which can prevent the wood from rotting and deforming after being exposed to rain or moisture (Figure 12(c)).
In summary, the above adaptive design technologies rooted in the same mother culture and natural environment make different types of buildings share a consistent spatial response. They are the common genes shaping the forms of Guangfu and Hakka ancestral shrines.

Conclusion and discussion
When two cultures confront each other in the process of diffusion, a geographical cultural transition zone may form. Correspondingly, the buildings in a transition zone can show different morphological characteristics that reflect the typical architecture in the original cultural region. By studying a large number of ancestral shrines preserved in Shenzhen, this paper analyses the spatial structure of their distribution and interlacing at the macro level and the variation in their morphological features at the micro level to reveal the generation mechanism of architectural forms in cultural transition zones. The main conclusions are as follows.
First, juxtaposition is an important mode of coexistence for architectural forms in cultural transition zones. This phenomenon can mainly be observed in regions dominated by a weak culture rather than a strong culture. By gathering densely in a small region, a weak culture can build up the ability to compete with a strong culture. This may constitute an important basis for achieving an equilibrium state in a cultural transition zone. Second, the integration modes of the architectural forms in the cultural transition zone are diversified, as represented in the changes in the combination structures of building groups, the alteration in the spatial pattern of single buildings, and the variations in architectural details and decorations. This leads to new architectural forms in the transition area that are different from those in the core area. It can be argued that if the change in the plane pattern is regarded as a transformation of cultural essence involving social organization, the shift in the construction details and decorations is a compromise regarding noncritical elements adopted by the weak culture to maintain its own characteristics. Finally, because of their shared human and natural environmental "genes", the buildings in the cultural transition zone exhibit foundational common features even while exhibiting heterogeneous material forms. It should be noted that one of the established backgrounds of this research is the existence of strong and weak cultures. It is the difference in cultural potential that led to the complex interlacing patterns of the Guangfu and Hakka ancestral shrines. This suggests that cultural potential may be an important variable affecting cultural interaction in transition zones, and diverse cultural intensity levels may produce different spatial equilibrium structures, which will lead to differentiated architectural forms. At the same time, the existence of the same mother culture gives the Guangfu and Hakka subcultures some similarities that may contribute to their cultural integration. If the variable of mother culture is controlled, will cultural conflicts in the transition zone become stronger, or will cultural fusion occur? This inevitably calls to mind the conflict and integration between different civilizations. Furthermore, the situation discussed in this article involves only two cultures. In reality, we often see the interlacing of three or more cultures. This makes the situation much more complicated because different cultures may develop their ability to compete with each other through strategic combination. Therefore, it becomes difficult to reveal the formation mechanism of the equilibrium state, and this is another issue worth scholarly discussing.

Disclosure statement
No potential conflict of interest was reported by the author(s).