Determination of Adjacent Visual Buffer Zones for the Temple Town of Chiang Mai City

Abstract

Buffer zone delineation often extends from the outermost edge of a site boundary for a specific distance. This study proposes a novel approach to determining the visual buffer for the temple town of Chiang Mai city. Adjacent Visual Buffer (AVB) was determined for the temples and their approaching routes using a GIS-based visibility method based on the viewing feature’s visual coverage and the observer’s visual range. The findings revealed that the total viewshed/visual range characterized the visibility of the temples in relation to the viewing feature’s height, resulting in AVB radii of varying sizes. The highest AVB radius of more than 200 m was found for temples situated in the city’s core, followed by those located on the city’s main streets and in isolated areas. The approaching route buffer was determined as a radius of 25 m from the road’s center. Interestingly, the density map results were consistent with the temple buffer results, indicating that the main roads of Chiang Mai’s historic area are highly used as an approaching route for temples. Combining the visual buffers of both temples and their approaching routes can aid in determining the level of control or guideline requirements in specific roads and areas.

1. Introduction

A buffer zone is “the immediate setting of the nominated property, important views and other areas or attributes that are functionally important as a support to the property and its protection” [1]. It represents a zone intended to protect heritage sites from negative impacts, as well as to enhance their core value. Visual impact remains a major issue for world heritage sites, especially those in the immediate setting of heritage properties. Intrusive built environments are the main factor affecting the distinctive character of historic districts and breaking significant skylines. According to a 2007 report, 73 out of 163 world heritage sites (44.8%) were given an “in danger” status due to poor management of buffer zones, while 26 sites (36%) had issues related to visual impacts in the buffer zone [1].

Today, dealing with the impacts of intrusive buildings remains difficult, particularly in areas adjacent to heritage sites. The issue of high-rise construction poses a major threat to the skyline of cultural heritage sites. Consequently, buffer zone delineation in historic urban landscapes has recently received much more attention. As the paradigm shift in heritage conservation has changed from protecting only property that carries values to extending to its relationship with natural and cultural aspects, as well as its surroundings, this has led to a broader sense of landscape territory. However, there are concerns regarding buffer zone management, especially for sites containing properties with diverse characteristics. Addressing other issues related to buffer zones has been suggested, particularly in defining boundaries appropriate to a site’s context.

Defining a buffer zone with an appropriate perimeter appears to be challenging. Several issues arise when questioning how far the boundary should be extended to ensure adequate protection of the core property from adverse impacts. In most cases, traditional buffer zones often delineate a specific distance of a 200–400 m radius around the property, depending on the state parties’ consideration of different aspects (e.g., the relevant authorities and management) [1]. However, one size does not fit all, as sites may contain properties with diverse characteristics—both tangible and intangible—within their territory. Within this context, several key aspects should be considered when establishing a buffer zone. The 2008 International Expert Meeting on World Heritage and Buffer Zones called attention to considering a given property’s aspects—including its size, components, and characteristics—as well as the type and characteristics of the potential impacts both from inside and outside the site. This meeting also emphasized the requirements of defining the key aspects of the outstanding universal value, authenticity, and integrity of a site to identify the appropriate size and shape for buffer zones. The Xi’an Declaration (2005) added the importance of inclusive spiritual and cultural aspects and emphasized that both urban heritage sites and their approaching routes require effective indicators to support land use that preserves significant skylines [2]. However, dealing with the impacts of intrusive buildings remains a difficulty, particularly in areas adjacent to a designated heritage site. Regarding the issues of high-rise construction, these posed a major threat to the skyline of the Royal Tombs of the Joseon Dynasty in Korea.

The recent Historic Urban Landscape concept has recommended focusing on visual integrity in heritage conservation and setting protection zones around sites in multiple layers regarding visual connections from the property to associative landscape features and vice versa [1,3,4]. For example, the Rhaetian Railway in the landscapes of the Albula/Bernina World Heritage Site, as described by Johann Mürner, is characterized by a large territory consisting of a railway line and landscape elements along the line (e.g., stations, sheds, platforms, and auxiliary technical structures) as the core property, while the entire mountain landscape serves as the setting that supports the site’s value. This site provides distinctive views that differ from each other: views of the highest gorges and the travel experience of technically advanced construction, as well as spectacular views of mountains, lakes, and side valleys. The site’s impact is related to visual aspects. The buffer zone determination considers the visual proximity of railway travelers, keeping in mind that the areas closest to the core property are the most important and therefore vulnerable to impacts. Consequently, the buffer is divided into three layers, primary, near, and distant zones, leading to regulatory and management systems that are implemented appropriately for each layer, with the primary buffer zone being more detailed and considerably more intense than the other zones [1].

For temple towns, Kyoto is among Japan’s historic cities, with 17 temples and shrines inscribed as World Heritage Sites. The buffer zone defined here considers the site’s visual focus and connection to the surrounding landscape so that temples are considered both visual attributes and viewing spots. The buffer boundary was established for each temple in multiple layers based on human visual perception by determining the close-distant view zone, which is a 500 m radius from the site to protect the view of the temple, while the far-distant view zone is an area that extends beyond to protect the view of the mountain landscape. The specialty of this buffer zone is that the close-distant view zone added the layer of a 20–30 m buffer area around the site and along the main route to the temple. Consequently, the overall area was designated as the temple view preservation control area, resulting in the temple serving as the baseline for historic townscape protection and the restriction of buildings’ architectural design and height limits at a low level. Additionally, this approach contributes to buffer zone management for socioeconomic benefits, as the buffer zone serves as a venue for local merchants and tourist attractions, as well as an area that supports the site’s carrying capacity [5,6].

In the case of Chiang Mai city, it has been recognized as a temple town. There are more than 400 temples in the city, with 38 active temples within the 2.5 square kilometer inner-walled area. Temples are the majority of the heritage properties on the list that have been proposed as tentative world heritage sites, along with the walled city, Doi Suthep Mountain, and Ping River, since 2015 [7,8]. This has resulted in the creation of a buffer zone for the historic site in the city through the CMWHI Project. Unfortunately, this is only a proposed buffer zone that covers a large boundary of approximately 183.12 square kilometer, which may contribute to the difficulty of its implementation according to existing regulations related to heritage conservation and local administration. Furthermore, many sites, including temples, do not have a buffer zone. Only 3 of the total 38 temples have been designated despite considering visual aspects, their significance, and their characteristics. This has led to having the same buffer size of a 100 m radius around each temple’s boundary, which may provide ineffective protection because the temples vary in size. However, the same maximum allowed height has been assigned to all buildings located inside the temples and within the wall. Moreover, as the temples in Chiang Mai are not singular buildings or features but rather groups of buildings and features surrounded by walls, adverse impacts may occur not only from outside but also possibly inside a site if control is ineffective. The buffer zone’s size and boundary may not need to be applied in a similar manner to all temples. Each temple requires a tailor-made buffer zone to meet specific needs in management due to its different characteristics, especially additional buffers to prevent potential threats occurring adjacent to the core property.

Visual aspects have become a key consideration in establishing buffer zone boundaries for historic sites. Empirical research has adopted visibility concepts using GIS-based analyses to explore past views [9] and determine them as a baseline to assess pre- and post-build impacts [10,11,12], resulting in the identification of visually sensitive areas, visual protection zones, or visual buffer zones around places of interest. Recently, a growing body of knowledge from prior research has revealed that areas adjacent to historic sites are highly sensitive to built impacts. Fang et al. (2021) assessed a district-scale area and found high sensitivity in the areas closest to dense historic buildings [13]. Similar findings arose in studies on visual integrity, highlighting that protection should be concentrated in areas adjacent to core properties and observer locations. Lee (2022) determined scenic zones for the historic district in Zhengding, China, as opposed to the existing buffer zones, considering the visual proximity between viewing objects and viewpoints. This study suggested that the highly sensitive areas around pagodas and tower buildings must be protected [14]. Sukwai et al. (2022) assessed buffer areas for building control by setting the sight lines from observers at the front gates of 38 temples within Chiang Mai’s walled city to specific heights of the mountain and suggested determining stricter control for the area closest to the wall [15].

Nevertheless, buffer zone delineation for temples still necessitates scientific visibility assessments based on their characteristics to determine the extent of management or control. Several studies have underlined the inside–out aspect. Visibility evaluations can be carried out from within protected sites [16] to support practical implementation and the effectiveness of present buffer zones [17]. However, most of the visibility research is undertaken from the observer’s perspective, even though the visibility of viewing buildings/features could potentially be favored in buffer zone determination. As demonstrated by findings from research on visual experiences, there is a relationship between a feature’s vertical size and visual distance. Particular structures can be seen at an optimal distance [18,19], and taller landmarks are seen by observers along approaching routes at farther distances [20].

For these reasons, this study aims to propose an approach to determining adjacent buffers for the 38 temples located within Chiang Mai’s historic walled city and their approaching routes, looking into the inside–out aspect while adopting a visibility analysis focusing on the characteristics of viewing features and visual perception.

2. Materials and Methods

2.1. Case Study: The Temples in Chiang Mai Walled City

Chiang Mai walled city is a nearly square-shaped area of approximately 2.5 square kilometers surrounded by walls and moats, located 3 km from the foothill of Doi Suthep Mountain, which is considered sacred to the city’s settlement (see Figure 1). It was part of the ancient Lanna Kingdom and was cautiously planned considering the animistic beliefs of the indigenous Tai and Lawa people, combined with Hindu–Buddhist concepts of cosmology associated with the sacred mountain. The walled city’s distinctive townscape is portrayed through the interlinkage between cultural heritages—mostly temples. Within the walls, there are 38 active temples that were built in different periods—during the time of the city’s establishment and in the early 20th century after the pagoda containing Buddha relics was built on Doi Suthep Mountain [21]. Temples can be classified according to their cultural significance and their role in holding ceremonies at the city and/or community level. Each temple was built for various purposes—as former kings’ residences, places to assemble people during pre-battle preparation, or places of worship and holding rituals. The temples in the walled city can be divided into royal and public temples, with only Chedi Luang and Phra Singh temple being royal temples, while the rest are public temples. The temples contain groups of buildings rather than singular structures.

The layout and zoning of the temples have also been influenced by cosmological concepts representing the universe (see Figure 2). The main vihara (the pavilion for religious ceremonies) was typically placed first following the main east–west axis and facing the eastern entrance of the temple, while the pagoda, representing Mount Sumeru, was subsequently placed and surrounded by other viharas in four directions, representing four sacred continents, with sand courts representing the ocean [22]. The main vihara and pagoda are located first near a temple entrance gate; this layout allows these features to be at the center point of the vista. Temples house Ratanataya’s genius loci, which includes Buddharatana (the Lord Buddha), Dhammaratana (the Buddha’s teaching), and Sangharatana (the Sangha or monks). As a result, creating a temple necessitates a location for learning about Buddhist activities and disseminating them throughout communities. It is also a venue where artisans can display their local fine art, sculpture, and architecture. The vihara and/or Ubosot are the primary elements in temple layouts that contain Buddha images [23]. Sumet Sumjai discovered in 1986 that most viharas and Ubosots face a body of water, replicating Lord Buddha’s enlightenment moment, in which he sat under a Bodhi tree facing the river. In the event that no waterbody was present, the Ubosot/vihara was oriented towards the east [24]. The fact that Ubosots/viharas face eastward is also in line with the Mahayana doctrine, which holds that the Nirvana image originated in western India. For Thai people, worshiping the Buddha image in an Ubosot/vihara is equivalent to worshiping the Nirvana Amitabha Buddha [25,26]. Ubosots facing east had a significant influence on the layouts of Chiang Mai’s temples as well. Parts of the major temples in Chiang Mai are arranged in accordance with the concepts of the Earth, heaven, and hell based on Trai Phum beliefs. For instance, Phra Singh temple’s Ubosot/vihara layout faces east. When locals worship its image, they also worship the pagoda, Suan Dok temple (the landlord temple), Suthep temple (the mountain-top temple), Jambudvipa (India, the origin of Buddhism), and the Amitabha Buddha (where Lord Buddha attained Nirvana). This configuration appears along the city–mountain axis. As stated in the study site description, Chiang Mai’s location was thoughtfully chosen since it is bounded by a body of water on the east and has a sacred pilgrimage route established on a mountain to the west [25].

As temples are valuable historic assets, there have been attempts to protect them by national and local authorities. The important buildings inside temples, especially pagodas and the main viharas, have been registered as national heritage sites by the Fine Arts Department for some temples. However, this registration only recognizes the buildings’ significance and ensures that their owners maintain their original appearance; it does not have control effects on other buildings or surrounding areas. In the case of Thailand, a buffer zone is established if it is required for the conservation of heritage assets. The legal basis for a buffer zone is determined by designating the surrounding area of a site at a specific distance, usually for religious sites.

In fact, buffer zones have been previously implied in the City Comprehensive Plan, which determined zones from the outermost edge of certain cultural and religious places in a single layer. According to the latest plan of Chiang Mai city (fourth revision, 2021), which is currently in the process of gathering public opinions [27], temples, especially those located outside the city center, were assigned the same buffer zone of 100 m around their walls regardless of their size and characteristics. Therefore, the temples within the historic walled city have yet to be addressed, with only three having the same buffer zone (i.e., Phantao temple, Chiang Man temple, and Duang Di temple), where the maximum allowed height is 12 m, no different from other buildings located within the temples and the walled city. As seen in Figure 3, the pagoda is the tallest building in most temples in the walled city. Their heights vary, ranging from 11 to 47 m, due to existing resources and their purpose as religious centers at the community or city level. The tallest pagoda is in Chedi Luang temple, measuring 46.77 m, but it would have been 88 m if it had not collapsed in 1545, which is believed to have been seen from the neighboring province. The shortest pagoda is in Dok Kham temple, measuring 11.03 m.

2.2. Methodology

As the literature review indicates, there are advantages to adopting the concept of visibility in determining adjacent buffers for the 38 temples within Chiang Mai’s walled city, as well as their approaching routes. Visibility analysis examines the ability of two or more locations to see one another. The maximum visibility of objects is influenced by various factors, including their vertical size and the conditions and techniques of observing [28,29,30,31]. Among various tools, GIS-based viewshed analysis is widely used not only to measure the visibility of buildings with variations in height [32] and to explore the extent of visual range coverage [33] but also to quantify visibility from a human perspective [34]. Conceptually, viewshed analysis enables the identification of visible areas derived from a digital elevation model (DEM) using an algorithm that can calculate the elevation between observer and viewing points. Because the calculation of visible areas defines visibility from or to viewing points according to the observer’s conditions [35] and viewshed calculation is dependent on the height of the viewing point [36], this study assumed that the total viewshed/visual range was characterized by the visibility of the temples in relation to the viewing feature’s height and the visual perception of observers on the approaching routes. The aim was to assess whether the total visual range was favored as a baseline for adjacent buffer zone determination. Finally, the findings were discussed by applying the terms of structural control/management and support for the existing boundary buffers. We employed visibility analysis tools in ArcGIS Pro 3.3 (ESRI Inc.) to assess the visible area from both aspects. We determined the main features of the temples as viewing points, while the approaching routes were used as locations to set the observer points. Therefore, the data input included the elevation surface and the location of the observer (see Figure 4). This study used a digital elevation model (DEM) with a resolution of 5 m × 5 m. The values input as the parameters considered visual perception, which was determined as described in the following sections.

2.2.1. Determination of the Viewing Points and Observer Locations

As this study intended to create adjacent buffers for the temple town, the viewing points were selected based on the significance of the landscape. In the case of Chiang Mai’s temples, the most important and tallest buildings are pagodas or the main viharas. In this study, pagodas were selected as the viewing features because they are the tallest buildings for most temples, except Methang temple, for which we used the main vihara.

The observer positions were located along the primary routes to the temples. In this example, we applied the angular distance, which is a distance less than one turning of the road from the temples [37]. A 500 m distance from the access point of the temples was set as the value for determining the location of the farthest observer point regarding the proximal line of sight distance from the viewer at which the built environment could be perceived [38,39,40]. For instance, the procedure counts the origin as 0 turns when the main gate of the temple is used as the origin. If there is a turning of the road within 500 m of the origin, it will be limited to one turn or 90 degrees of angular shift (a 45-degree junction counts as a 0.5 turn). In this study, approaching routes are defined as routes that connect directly to the temple gate (the access point) with less than one turn and over less than 500 m.

2.2.2. Determination of the Adjacent Visual Buffer for the Temple Site

An adjacent visual buffer (AVB) was created based on the tallest building’s visibility. As visibility is determined by the tallest building on the site, we selected either the pagoda or the vihara as the viewing feature based on which one was tallest and inputted their height in the form of a feature offset. The analysis used pagodas as the viewing features for most of the temples studied except Methang temple. Moreover, given that the total visual range was concerned with the visibility of the pagoda/vihara, a 1.6 m surface offset was added to account for the position of the average eye level of an adult to identify the visible area of the given features, and the vertical angle of the observer view was set at 10 degrees to consider the normal line of sight of people standing without eye rotation. Finally, visibility was assessed in the area of 360 degrees around the site to focus on the visual range of the given places (see

Table 1. The parameter values input in determining the adjacent visual buffer for a temple site.

Classification	Representation of	Value
Surface offset	Human’s eye-level	1.6 m
Feature offset	Viewing point	Height of pagodas/viharas
Azimuth 1, 2	Horizontal plane	360 degrees
Vertical plane	Vertical angle (sight line of people standing)	10 degrees

).

2.2.3. Determination of the Adjacent Visual Buffer for Approaching Routes

The approaching route determined the observers’ locations. Thus, the visual buffers were created based on the visual perception of an observer. In this case, the value input for this parameter considered their visual limitations, which determined the values for the maximum line of sight and visual angle in regard to the mode of activity. According to human perception, object recognition is concentrated at the center of the field of vision and covers about 20–60 degrees of binocular view. The highest degree of acuity in the range of about 20–30 degrees of binocular view can distinguish the shape and texture of objects in the landscape. Therefore, we set the value of the visual field to 30 degrees [41]. Several observer points were set with a 90 m distance between points, considering the distance that a pedestrian walks within a minute. Finally, the visual range of the observer was determined at 100 m for sightline distance, as suggested by studies on urban street views [20,42,43], for creating the buffer radius from the road’s center (see

Table 2. The value to input in the parameter in determination of adjacent visual buffer for the approaching route.

Classification	Representation of	Value
Observer height offset	Human’s eye-level	1.6 m
Horizonal plane	The center of the field of vision	30 degrees
Maximum distance	Sight line distance	100 m

).

3. Results and Discussion

An overview of the visual buffering zones is displayed on the AVB map. For an AVB, the visual angle is used to determine the built elements in the buffer zone. This implies that only specific areas adjacent to the landmark require strict control but not the entire historic limit of the city moat/wall. This is notably distinct from boundary buffering, which is caused by the varying heights of the landmarks (see Figure 5). The AVBs of the temples partially show a cluster of buffers along the east–west axis. Pa Phrao Nai, Dab Pai, Ratchamonthian, Khuan Kha Ma, Mo Kham Tuang, Saen Mueang Ma Luang, Chiang Man, and Lam Chang are the major temples located in the northern section of the area. This cluster has a moderate AVB radius and is significantly distinct from the central temple cluster. Prasat, Pha Bong, Sri Koet, Tung Yu, Chai Phrakiat, Intakhin, Duang Di, Phan Tao, Chedi Luang, Pan Ping, Umong Mahathera Chan, Samphao, Phan On, Muen Lan, Dok Kham, Dok Ueang, and Pha Khao are part of the center cluster. This cluster features the highest amount of overlapping AVBs and the largest number of temples clustered together. Most of them lead to Rajadamneon Street, the main street in Chiang Mai’s historic district. Methang, Muen Ngoen Kong, Phuak Hong, Phuak Taem, Phrachao Mengrai, Phan Waen, Chang Taem, Muen Tum, Chet Lin, Fon Soi, Sai Mun Mueang, and Sai Mun Phama are part of the southern cluster. The local community’s temples are strongly represented by this cluster. They are dispersed over the southern section and have less overlap between AVB zones. The alignment with the east–west axis is a common characteristic throughout all clusters. Differential AVBs influence the protection boundary and suggest a special method for safeguarding the property sites in accordance with this. The map presented in Figure 6 illustrates the overlap of the buffering, indicating that certain areas may necessitate varying degrees of invasive element management.

As expected, the results correspond with the height of the temple sites (of their pagodas/viharas) in accordance with the AVB radius approach. According to

Table 3. Results on adjacent visual buffers for temple sites.

Temple No.	Name	Object Height (m)	Adjacent Visual Buffer Radius (m) (AVB Radius)
1	Pa Phrao Nai	14.73	73
2	Dap Phai	14.06	73
3	Prasat	13.64	66
4	Pha Bong	14.47	70
5	Phra Singh	34.90	189
6	Muean Ngoen Kong	14.80	75
7	Phuak Hong	21.66	114
8	Phuak Taem	22.78	120
9	Phan Waen	17.00	86
10	Phrachao Mengrai	14.58	75
11	Chedi Luang	46.77	250
12	Sri Koet	18.82	100
13	Thung Yu	21.29	115
14	Khuan Kha Ma	18.97	100
15	Ratchamonthian	23.00	122
16	Mo Kham Tuang	20.50	107
17	Saen Mueang Ma Luang	28.95	155
18	Chiang Man	21.60	110
19	Lam Chang	20.63	108
20	Pan Ping	26.73	141
21	Dok Ueang	17.26	85
22	Dok Kham	11.03	55
23	Umong Mahathera Chan	17.68	89
24	Duang Di	17.42	89
25	Chai Phra Kiat	19.53	99
26	Phan Tao	13.80	68.75
27	Chang Taem	19.81	104
28	Pha Khao	14.28	71
29	Muen Tum	20.71	108
30	Sai Mun Mueang	16.73	86.25
31	Sai Mun Phama	14.41	73
32	Fon Soi	18.14	94
33	Chet Lin	14.76	77
34	Phan On	18.54	93
35	Muen Lan	16.31	83
36	Samphao	12.71	62.25
37	Intakin	16	80
38	Methang	12	57.25

, the temples range in their AVB level from 55 to 250 m, with an average of 98 m. Chedi Luang temple (No. 11), which was designed to serve as the primary landmark in Chiang Mai’s historic region, has the highest AVB radius at 250 m. The AVB in this temple is the only one that is higher than 200 m. As seen in Figure 6, Chedi Luang temple is situated in the city’s core. Phra Singh temple and Saen Mueang Ma Luang temple, at 189 and 155 m, respectively, are the second tallest temples that have AVB radii higher than 150 m. Nevertheless, a high AVB is also indicated for Saen Mueang Ma Luang’s pagoda strangely. An explanation can be found in this temple’s former role as the city’s primary open space landmark (Saen Mueang Ma Luang is also known as “Kuang Luang”, meaning main open space). Temples can be found all across the historic district within an AVB range of more than 100 to 150 m. Most of them are located on Chiang Mai’s main streets, such as Rachadamneon, Phrapokkhao, and Singharat. In accordance with the AVB map, the primary role of these streets is to provide transit in Chiang Mai’s historic area. The temples in communities or in Chiang Mai’s isolated areas are those that have AVB radii of less than 100 m. Rather than implying the significance of temples per se, AVBs are focused on a visual evaluation in order to establish buffer zones that safeguard historical sites like pagodas, Ubosots, and/or viharas, which are dependent on their finest attributes.

The approaching route results indicate two aspects of buffer determination. First, most temples have approaching routes on the eastern front, especially large temples such as Chedi Luang, Phra Singh, and Saen Muang Ma temple (see Figure 7). The other aspect is the intensity of the overlaid approaching routes for all temples, as shown in Figure 8. The intensity was calculated using the visual range as the buffer determination tool along the road. The approaching route buffer shows a radius of 25 m from the road’s center. The intensity of the approaching route map displayed repeated buffering on the same routes. As shown in Figure 8 (right), the main roads in Chiang Mai’s historic area, such as Rachadamnoen (center east–west axis), are highly used as approaching routes for temples, as well as Prapokklao Road (right north–south road). Consistent with the AVB map, the temples clustered along these roads affect the intensity of the route buffers. The intensity of the visual buffers for approaching routes implies the level of control or guideline requirements for specific roads (high-intensity roads). The intensity map evidently recommends the level of conservation needed as supportive view protection along these roads. Nevertheless, it suggests that some roads require more intensive regulation than others; on non-intense roads, a lower intensity of regulation may be allowed as well.

Comparison Between the Boundary Buffer and the Adjacent Visual Buffer

The comparison results for the boundary buffers and the AVBs show considerable differences in their radius and size ranges. Figure 9 depicts a boundary buffer with a fixed radius set by the temple site’s boundaries (land plot). The AVB, on the other hand, is established according to a assessment of the view of the most important heritage elements, such as the pagoda, Ubosot, and vihara. The majority of the AVB radii are included within the boundary buffer radii, with the exception of Chedi Luang, Phra Singh, and Saen Muang Ma Luang temples, which have greater radii. These temples require a wider buffer radius based on their heritage’s height. In some temples, a bigger radius suggests that the uniform radius of the boundary buffer may lead to the underprotection of the properties, whereas a smaller radius implies that the properties are excessively protected.

Nonetheless, the genuine advantage of the AVB depends on the buffer’s origin and its intended usage as a view protection mechanism. AVBs are implemented differently than boundary buffers or uniform control, such as building height regulations at a maximum of 12 m. The AVB requires angular control over the area adjacent to the heritage origin site. As shown in Figure 10, the example of Phra Singh’s AVB demonstrates the significant use of the AVB in 3D assessment. It provides reasonable control by utilizing a protection cone (the AVB’s inverted cone) as the control determination area. An example of an intrusive structure is the mass structure, which nevertheless encroaches on the AVB despite it being limited to 12 m in height by the boundary buffer. However, in the AVB evaluation, some significant parts of the temple were also identified as intrusive structures, but in terms of historical preservation, harmonic elements of the temple may be allowed to intrude on the AVB.

Finally, this comparison of the buffer evaluations is intended to encourage and strengthen the conservation of heritage buffer zones. While a boundary buffer can provide uniform generic protection based on the radius of a land plot, an AVB can specify the strength of heritage buffer protection based on its radius and proximity to heritage. These specific and generic buffer protections can support and promote the prevention of encroachment on cultural sites.

4. Conclusions

This study presented an alternative method for determining the radius of buffer zones based on a visual assessment of angular and viewing distances. Its results support an approach to safeguarding historical sites that serve as landmarks and are characterized by pagodas, Ubosots, or viharas. The findings demonstrate an adjacent visual buffer’s (AVB) capabilities in identifying a buffer zone for such locations. In comparison to the traditional boundary buffer, which is defined by a radius of 100 m from a heritage site’s boundary for all properties, the AVB uses 3D studies to generate a more appropriate proportional radius. It reveals different radii based on the height of the heritage sites rather than static buffering from a property’s boundary. These outcomes demonstrate how 3D modeling can be used to analyze heritage visual protection. This study’s proposed methodology can be applied to any heritage site that has a connection to a significant feature.

This study also examined the approach routes to heritage sites to evaluate and propose buffer zones according to street (continuous line) patterns. Using the visual range, which is concerned with the visibility of observers in sequence, as the method for the streets, the outcomes show the probable radii for buffer zones from the center of approaching routes. Regarding view preservation in heritage, a buffer from the approaching route serves as a supportive buffer, in which the design of building structures should be in conjunction with the temple and the core area should remain accessible in key view at the end of a route.

The results of this study suggest that the AVB zones should incorporate intensive intrusion protection. For example, while building zoning law limits the construction height to 12 m within a boundary buffer zone of 100 m, AVBs may require more intensive measures in the established buffer zones. These could include stricter control of buildings’ features (e.g., lower height limits, color, material, massing, style, and form) or any structure that may encroach on the landscape and the historical context, along with the approach routes, to create a cohesive landscape for heritage areas.

According to this study, it is necessary to have a buffer zone that is consistently connected to the heritage site. While the boundary buffer zone provides generic protection that might not seem relevant in any physical context, this study’s proposed AVB protection may strengthen it. Furthermore, another heritage interlink that may be understudied in terms of buffer zones and linkage landscapes consists of the overlap between buffer areas. Three-dimensional analysis and visualization will be useful to study further, with an example being the 3D visualization displayed in this article.

The determination of buffer zone boundaries is critical for effective protective measures. The proposed methodology for determining visual buffers in this study revealed differences in the buffer sizes for each temple using a visibility analysis. The maximum visibility of viewing features is based on the relationship between their vertical size and distance. This approach can be advantageous in buffer zone determination, particularly if protection is needed for adjacent areas or if additional buffers for intensive protection are required. However, it is important to note that this method does not guarantee protection of the core property from adverse impacts other than visual impacts. Future studies could address these limitations by considering additional factors that may affect heritage sites beyond visual aspects.