Zoning scenic areas of heritage sites using visibility analysis: the case of Zhengding, China

ABSTRACT The preservation of historical architecture not only protects the specific building site but also preserves the surrounding historical setting. However, unassigned and vast historical settings are considered extremely delicate in terms of conservation. The formation of a Scenic Area provides a legal method of protecting the historical setting of cultural heritage sites in China. Additionally, scientific zoning of the Scenic Area can create zones for restricting construction and development. This article shows the process of rationally determining the Scenic Areas analyzing the visibility of Geographic Information System (GIS), taking the example of the seven National Heritage Sites (NHS) in Zhengding County, China. The objects of the visibility analysis included five high-rise architectural heritage buildings: pagodas and towers from the seven NHS and three other viewing points on the city walls to observe these sites. The results revealed several highly sensitive areas between the architectural heritage sites, in addition to the predicted areas of concerns near heritage sites. Therefore, the Scenic Areas were zoned as large connected areas by combining the spaces between the NHS. This study will help achieve rational zoning for sustainable conservation and development of high-rise cultural heritage sites forming a historical urban landscape.


Introduction
Historical architecture can be found in various cultural and natural settings. Such architecture is preserved to protect the architecture and the surrounding historical setting. "The Venice Charter" defines a historical monument as a single architectural work in an urban or rural setting (ICOMOS 1964). The proper conservation of the setting further enhances the value of the heritage, particularly when several historical sites are in proximity. However, the demand for urban development due to rapid economic development is also justified, and it is necessary to adapt to the changing shape of cities in the 21st century by accepting the demand.
For example, Zhengding County in Hebei Province, China, has several National Heritage Sites (NHS), including temples, pagodas, and shrines, inside the old city, which was a large city until the end of the Qing Dynasty . Many of historical cities developed into modern cities in the 20th century, and lots of old buildings in the cities were destroyed under the development process in China. Unlike that, since Zhengding managed to stay out of the trend of development of modern cities (Huimin 2006), the NHS and the historical setting embracing the heritage sites, including the urban fabric and old buildings, remain relatively well-preserved. Further, these historical heritage develop tourism and boost Zhengding's economy (Hongliang 2019).
However, like other cities in China, Zhengding faces rapid urban construction in the 21st century. In terms of conservation, these unassigned and large historical settings are in such a delicate condition that they may be quickly replaced by a group of skyscrapers. This leads to the destruction of the historical urban setting around the NHS and loss of valuable economic resources. For high-rise historical architecture, such as pagodas or towers, the landscape value is considerably lost when they are surrounded by high-rise modern buildings rather than low-rise historical buildings. Therefore, the preservation of the setting and heritage sites should be carefully considered.
The preservation of historical urban settings and the acceptance of urban development has two objectives. This can be realized through the formation of a "Scenic Area" suggesting the placement of highdensity constructions and construction restrictions around heritage sites. The Scenic Area may be constructed to protect the designated heritage site along with the "Protected Area" under the "Law on the protection of cultural heritage of the people's Republic of China" (2017a). The Chinese text of the term "Scenic Area(建设控制地带)" implies "area for controlling constructions." Detailed construction control requests, including the volume, height, color, shape, and other aspects of the building, are made in the Scenic Area (2004a). Among these requests, the most effective is regarding the building's height control, in terms of landscape value preservation of highrise historical architectures.
For example, the Scenic Area should be appropriately zoned around a tower because controlling the height of the buildings built around the tower can highlight its landscape value. However, if a certain area has several towers and people can climb one of those to view the others, the zoning of the Scenic Area around them requires further scientific analysis. Therefore, height control request is required not only for a certain area around the tower, but also for the visible areas between towers. Visibility analysis can be used as a valuable tool for constructing the Scenic Areas.
Regarding visibility in heritage, Garden (2006) stated that the three principles, based around ideas of (i) boundaries, (ii) cohesion, and (iii) visibility, create the "heritagescape," among which "physical visibility is the method for recognizing the tangible features creating a cohesive site and identifying the physical limits of a site." (Garden 2006) From a technological perspective, Benedikt (1979) studied visibility analysis through the concept of "ISOVIST." Since then, the scope of research and its application on visibility is increasingly broadening, as techniques to quantify visible points constantly diversify (Benedikt 1979). Smith, Goodchild, and Longley (2007) address the full spectrum of spatial analysis and associated modeling techniques that are provided within the framework of geographic information systems (GIS) and related software (John De Smith, Michael, and Goodchild 2007). In studies related to historical heritage by Agapiou (2015) and Elfadaly (2020), GIS is primarily applied to multidisciplinary management of heritagerelated information and observation of its changes (Agapiou et al. 2015). André Soares (2019) presented a methodology to assess the protection zones of urban cultural heritage using a co-visibility analysis tool evaluating the visual range from a heritage site in a 3D city model (Lopes et al. 2019).
The visibility analysis of Chinese cultural heritage reflects the need to preserve a heritage and develop structures around it. Xiao Shizhen, Xiao Hua, and Wu Yuhui (2019), as well as Wang Xiaohui and Huang Yong (2013), analyzed the visibility to assess the impact of building tourist facilities in landscapes containing valleys or lakes (Xiao, Xiao, and Wu 2020). Additionally, Kou Xin and You Tao (2014) presented Scenic Areas of each cultural heritage through visibility analysis. However, none have dealt with the mutual visibility of multiple cultural heritages in an area (Kou and You).
Taking the Zhengding old city as an example, in this article, we present a visibility analysis using ArcGIS to provide reasonable grounds for zoning Scenic Areas in locations where architectural heritage sites, such as pagodas and towers, are located close to each other. Visibility analysis adds a new scientific layer to the existing grounds for zoning, for instance, the distribution of historical buildings and old urban fabrics around the NHS. This will help determine the areas for development, in harmony with preservation of cultural heritage.

History of seven NHS in Zhengding
Zhengding County is located in the north of Shijiazhuang City, southwest of Hebei Province, China. (Figure 1) Shijiazhuang -originally built as an emerging industrial city due to the construction of a railroad that began in the early 20th century -is the current provincial capital of Hebei Province. However, from the 7th century to the end of the 19th century, Zhengding was the political, economic, and cultural center in the central and southern parts of Hebei. (Youheng and Pinglan 2020) Although Zhengding was an extremely prosperous city called the "Strategic Hub city of Hebei" (Shuizhu 2003), it did not undergo a drastic transformation into a modern and contemporary center as the nearby Shijiazhuang, which developed as a regional center (Huimin 2006). Consequently, Zhengding was underdeveloped in terms of urban development, even though the historical constructions of the old city remained, such as the city walls, urban fabric, and temples.
Among the remaining historic buildings in the old city of Zhengding, a total of eight were designated as NHS before 2018, including the Longxing Temple, Longxing Temple was built in A.D. 586 by the Sui Dynasty. It was reconstructed in the Song Dynasty (11 th century), forming a huge layout of the north-south direction with Dabeige as the main Hall. To date, many wooden buildings of the Song Dynasty remain in the temple. Additionally, the Dabeige, which was restored in 1989, is the highest wooden building with three stories (Youheng 1998).
Kaiyuan Temple is the only existing Tang dynasty (8 th century) Buddhist temple where the bell tower and pagoda are arranged symmetrically in China, and the remaining pagoda was reconstructed in the Tang Style during the Qing dynasty (17 th century) (Lianshun, Xiuzhen, and Yujie 1994). Each of Tianning, Linji, and Guanghui Temples have their own unique type of pagoda, although no historical wooden buildings remain in the temples. In the Confucian Shrine of the City, many of the buildings that used to exist in the past are destroyed, and only the front gate of the Yuan Dynasty (14 th century) still stands (Xiaoli and Songlu 2006). Fengdong Stele records the meritorious deeds of Li Baochen, who ruled Zhengding during the Tang Dynasty (8 th century) (Lingdi, Ruiping, and Du 2005). (Table 1) Zhengding's road layout consists of an east-west road connecting the east and west gates, and two north-south roads that lead to the south and north gates, which are called the "double-crossed roads." This layout was constructed in the 15 th century, and its surroundings flourished during the Qing Dynasty (Xianchao 2017). The old road layout continues to be used, and historical buildings remain relatively concentrated near the south gate of Longxing Temple at the east end of the east-west road and near the south and west areas of Kaiyuan Temple. (Figure 2)

Landscape value of NHS in Zhengding
Each of the seven NHSs in Zhengding have historical and artistic significance in terms of their relationship with the old city. First, Zhengding has maintained the historic urban landscape, as the remains of the old city walls and the urban fabric inside it are still extant. The bricks on the outer surface of the city wall were almost lost, but the inner wall, which was piled up layer wise by pounding the soil (Jindong and Du 2003), continues for approximately 8 km throughout the city (Youheng  (Xiaoli and Songlu 2006). 7 (Lingdi, Ruiping, and Du 2005).
and Pinglan 2020, 46). The presence of the city wall has played an important role in maintaining the essence of the old city in Zhengding. Old buildings remain scattered throughout the city, and they are mostly clustered around Longxing Temple and Kaiyuan Temple. Second, NHSs are relatively concentrated in the central and southern parts of the old city. Yanzhaonanda street is a major north-south street in the old city, which starts from the South Gate Tower at the southern end of the street. Guanghui Temple, Linji Temple, Kaiyuan Temple, Fengdong Stele, and the Confucian Shrine of the City are located along the street to the north. Zhongshan road crosses Yanzhaonanda street, which runs from the West Gate of the city to Kaiyuan Temple, Tianning Temple, and Longxing Temple in the east. The area covered by the Yanzhaonanda street and Zhongshan road is the center of the old city, where all the NHSs are located. Additionally, this area's historical urban fabric is comparatively well preserved than the north.
Third, high-rise NHS, such as pagodas, towers, and pavilions, dramatically transform the city's skyline. The old city of Zhengding was often described as "nine pavilions, four pagodas, and eight large temples," (2020) which indicates that the pagodas and pavilions were elevated against the backdrop of low-lying buildings, creating a beautiful urban landscape. The nine pavilions point to the four gate towers, four corner towers above the city wall, and the pavilion at the center of the city. All the wooden gate towers on the wall have been destroyed, and only some of the walls remain; the South Gate Tower was recently restored (Youheng and Pinglan 2020).
The four pagodas include the Kaiyuan pagoda, Lingxiao pagoda, Hua pagoda, and Chengling pagoda, while the eight large temples include the Longxing Temple and the four temples above which the four pagodas are located, as well as Chongyin temple, Hongji Temple, and Sheli Temple, which were destroyed (2020). Although some of the high-rise buildings are not extant, the existing high-rise NHSs continue to create a historical and artistic urban skyline due to their varying building types, shapes, and construction periods. Several pagodas or towers were designed to climb up inside, so they serve as an observatory for the entire old city (Youheng and Pinglan 2020). (Figure 3) Rarely in China is the historic urban skyline maintained so well. Several high-rise historical architectures are located close to each other. People can climb up these structures to take in the city view; even the historic urban setting is well maintained. Through the above features, we understand that the value of seven NHSs of Zhengding is not only in "a single architecture" but also in "the historical urban landscape created by all architectures." Therefore, in the zoning of the "Scenic Area" to protect the NHS, the protection of the entire historic urban landscape should be considered, rather than considering the NHS as a lone architectural heritage site.

Evaluation of the existing scenic area
The designation of heritage sites in China must be set as the Protected Area for the protection and management of these sites, and a certain zone surrounding the site may be set as the Scenic Area in accordance with the "Law on the protection of cultural heritage of the people's Republic of China" of 1982, as mentioned above (2017b).
According to Article 13 of the "Implementation Regulations of the Law on the protection of cultural heritage of the people's Republic of China," the scenic area of cultural heritage refers to "the area surrounding the protected area of the cultural heritage, restricting constructions to protect the safety, setting, and historical features of the cultural heritage." (The Standing Committee of Chinese People's Congress 2017) Regarding restrictions on construction activities within this area, the law comprehensively stipulates that construction processes not related to the protection of the heritage are not permitted, except those undertaken in special circumstances of the Protected Area, and any construction process within the Scenic Area should not pose a threat to the safety of heritage, nor should it affect the historical setting (2017c).
The implementation of the Protected Area and the Scenic Area were specified when the "Requirement for the conservation plan of NHS" was enacted in 2004. According to this, the Scenic Area may be newly zoned or revised to ensure the integrity and harmony of the environment around the NHS and may be zoned into various types according to the difference in management and construction restrictions (2004b).
After the Law was enacted in 1982, each local government established the zones for their heritage. The initial zones were often set according to the scope of the existing architecture or the convenience of practical management, rather than being based on the historical scope of the heritage and systematic analysis of the surrounding environment due to the time and human limitations. Therefore, the Scenic Area is typically not fully surrounded by the protected area or grouped into one, without being divided into types according to the requirement.
The earliest zones of the seven NHSs in Zhengding were individually disseminated by the People's Government of Hebei Province in 1992 (People's Government of Hebei Province 1992a), as shown in Figure 7(a).
In the case of the Liangxiao Pagoda of Tianning Temple, the zoning of which was conducted in 1992, the Protected Area is 5 meters eastward to the pit, 71 meters southward to the Zhongshan-road, 5 meters westward to the east fence of the private house, and 6 meters northward to the private house, based on the outline of the lower part of the fence. The Scenic Area is 23 meters eastward, 35 meters westward to Zhenzhou street, and 56 meters northward to the coal yard, based on the outline of the Protected Area (People's Government of Hebei Province 1992b), as shown in Figure 4(a).
The Lingxiao Pagoda is 41 m high (Jindong 2002). This pagoda is considered a monumental building because it is in the center of the city and is visible from many locations. However, the Scenic Area is excessively narrow considering the significance of the urban landscape. Studies indicate that the necessity for a large Scenic Area was not recognized at the time due to the relatively low urban density. However, this necessity was soon recognized when in 1998, the People's Government of Zhengding County formulated a "Medium-to-Long Term plan for the protection and use of the cultural heritage sites of Zhengding," and newly zoned the areas for NHS (People's Government of Zhengding County 1998).
According to the Law, which was officially validated in 1992, the zone of the NHS must be ratified by the provincial governance (The Standing Committee of Chinese People's Congress 1991). However, since the zone that was divided in 1998 is very different from that of 1992, it calls for a comparison between the two. The Protected Area has not changed much from before, except for the southern area, and the Scenic Area extended 160 meters to the east, 63 meters to the south, 35 meters to the west, and 130 meters to the north from the protected area, covering almost one block (People's Government of Zhengding County 1998), as shown in Figure 4(b).
In order for Scenic Area to protect the historical background of cultural heritage, the Scenic Area has an appropriate width and completely surrounds the Protected Area. In the case of the Lingxiao Pagoda, a comparison between the zoning of 1992 and 1998 suggests that there were problems with determining the Scenic Area beyond the southern Protected Area and the appropriate width of the Scenic Area. The resultant expansion of the northeastern Scenic Area in 1998 reflects the changed perception of concerns over rapid urban changes and the destruction of the urban landscape, along with attaching significance to the scenic role of the Lingxiao Pagoda. However, whether the entire block should have been expanded and why the southern and eastern areas were not included in the expansion plans remain questionable. Similar situations are seen in other NHSs, as shown in Figure 7(a). In addition, in the case of Longxing Temple and Kaiyuan Temple, consideration of the historical buildings and urban fabric that remain near the temple is not reflected in the Scenic Area.
These situations show that scientific analysis of the extent to which the landscape is affected is needed for rational adjustments of the Scenic Area. This Scenic Area, planned before the "Requirement for the conservation plan of NHS" was enacted in 2004, must be revised through a research based on a value analysis of the architectural heritage. Therefore, through the analysis of visually sensitive areas affecting the view between the high-rise architectural heritage and the historical skyline, we intended to determine an appropriate Scenic Area for each architectural heritage.

Visibility analysis
In visibility analysis, we began with the selection and classification of valid analysis objects. We then identified the range of visual sensitivities for each object and between the objects and analyzed the visual sensitive areas comprehensively by summing them up.

Selection and classification of valid analysis objects
We set two principles for selecting the objects of analysis. First, we determined the objects for the high-rise NHS. The architectural heritage, which is higher than the general architecture, becomes the object of a distant view and forms a historic city skyline. Among the NHS, Fengdong Stele is 2.3 meters high (Lingdi, Ruiping, and Du 2005, 55); the roof top of the front gate of Confucian Shrine, a single-story wooden building, is 9.13 meters high (Xiaoli and Songlu 2006); and the roof top of a traditional building in Zhengding is typically lower than 10 meters. By comparison, the four pagodas stand out in the old city because each of those pagodas is more than 30 meters. Additionally, Dabeige, the tallest building in Longxing Temple, stands tall among the low-rise buildings with a total height of approximately 33 meters (Committee for compilation of Annals of Hebei Province 1994). The Confucian Shrine of the City and Fengdong Stele are located near high-rise NHS; thus, they are considered together in the zoning of the Scenic Area, but are excluded from the visibility analysis because they are not prominent in the city skyline.
Second, we determined the viewpoints to see an NHS. Some viewpoints are not in an NHS but can reveal the landscape value of the NHS in the old city. The historic sites of the West Gate, North Gate, and South Gate towers were designed to climb from inside the city walls; thus, they can serve as viewpoints for predicting the historic landscape of the NHS. Among them, the South Gate tower was recently restored to provide a dramatic view of the southern part of the old city (Youheng and Pinglan 2020); moreover, a high-rise South Gate tower enriches the historical skyline. The old City Wall of Zhengding was designated as a Provincial Heritage Site (PHS) (Jindong and Du 2003) and is expected to be restored in the future; thus, the urban view needs to be considered from this point to form the scenic area.
Based on this principle, there are eight selected analysis objects, including four pagodas, one pavilion at Longxing temple, and three city gate tower sites. These analysis objects can be divided into three categories in terms of the roles of the landscape.
First, the point not only serves as an object of view but also as a viewing point for other points located inside. These include the Dabeige of Longxing Temple, Lingxiao Pagoda, Hua Pagoda, and the South Gate tower, and they are marked in uppercase letters, like "A," from A to D.
Second, the point serves as an object of view but does not serve as a viewing point for other points because there is no access to climb up the building. This includes two pagodas: Kaiyuan Pagoda and Chengling Pagoda, and they are marked by lowercase letters, like "a," from a to b.
Third, the point is not an object of view because it does not have restored buildings, but it is a high-level viewpoint, like the historic sites of the North Gate and West Gate, which are marked as "a'" and "b'." These are shown in Table 2.

Methodology of visibility analysis
The cadastral maps of Zhengding in the 2000s describing urban structures were critical about creating the city model. ArcMap software of ArcGIS was used to generate NHS and city walls and buildings and analyze their visibility. We set the following process for the visual sensitivity analysis of object points: Step 1. Two premises 1. The straight line from the viewing point to the viewed object: the closer the line, the higher the visual sensitivity.
2. The viewing point as the center of the circle: the closer to the center, the higher the visual sensitivity.
Step 2. The sum of the two premises. The visual sensitivity around the analysis object is calculated by adding premise 1 and premise 2. The straight lines that connect the eight viewed objects (A, B, C, D, a, b, a', and b') from the viewing point are the direct visual lines. "Premise 1" implies that the closer a tall new building is placed to these lines during the urban development, the more interference it causes in viewing the object from the viewpoint. The observer's field of vision forms a fan-shaped field of vision in 2D. The angles generate a nearperipheral vision of 60° and a mid-peripheral vision of 120° (Peripheral Vision 2021). This study does not find the visual field around one point; rather, it finds the mutual visual field between the two points. Therefore, the visibility around it is analyzed based on the straight line of sight between the two points. Since the average eye height looking at A, B, C, and D is about 20 meters, the most visually sensitive range on both sides of the straight line between the two points is 20 meters, and 200 meters is set as the scope of analysis and divided into five. The visual sensitivity range was set to 20 m, 50 m, 100 m, 150 m, and 200 m on both sides of the straight line. Figure 5(a) shows a line connected from the viewpoint to the viewed object; however, as there is no view object, a' and b' do not connect to each other.
"Premise 2" indicates that the closer a new high building is placed to the center of the circle during the urban development process, the more interference it causes in viewing the object from the viewpoint. Since this range is an indirect visual range compared with the direct visual line between the two points specified in "Premise 1," it is necessary to determine the sensitivity of all parts of the city by setting the scope relatively wider. Therefore, the maximum range was set at 1,000 meters and divided into five. In this analysis, excluding a and b, six viewpoints (A, B, C, D, a', and b') were centered, with a range of 100 m, 200 m, 400 m, 700 m, and 1,000 m radius as the visual sensitivity range, which is demonstrated in Figure 5(b). Figure 6 is the result of calculating the visual sensitivity around the objects by adding the two sensitivity ranges. In the picture, red is an area with a high visual sensitivity, and green represents an area with a low visual sensitivity.

Results of visibility analysis
The results of this analysis identified some of the expected visual sensitive areas. The central and southern regions of the old city were expected to have high visual sensitivity due to the concentration of high-rise architectural heritage, as shown in the analysis results. In particular, the area around the Lingxiao Pagoda was expected to have high visual sensitivity because it is in the center of the city. Additionally, the results of the analysis showed that this area was the most visually sensitive area, as many visual lines overlap this Pagoda.
However, the analysis revealed that there were several unexpected areas of visual sensitivity, implying that there were areas with high visual sensitivity, even though they were not adjacent to the highrise architectural heritage ( Figure 6). The areas were as follows: These are the areas where at least two visual lines from viewpoint to high-rise architectural heritage overlapped and were located either in front of or behind the heritage on the visual line. The analysis results showed the areas to be considered when zoning Scenic Areas to limit the height of urban construction.

Zoning the scenic areas of NHS
The basic considerations for the effective preservation of the values of single NHS, before reflecting the visual sensitivity in the zoning of the Scenic Area, are as follows. The zoning of the Scenic Area should surround all sides of the Protected Area without omission and have proper width. Therefore, a new Scenic Area should be established around the Confucian Shrine of the City and the Fengdong Stele, which previously did not have any Scenic Area, and should be added to the south of the Protected Area of the Longxing Temple, Tianning Temple, Linji Temple, and Guanghui Temple, and the south and east of the Kaiyuan Temple. In addition, the Scenic Area east of Longxing Temple does not have sufficient width; thus, it should be extended to the outward. The southwestern area of Longxing Temple and Kaiyuan Temple is adequately preserved in the historical urban fabric and traditional buildings; thus, when zoning the Scenic Area, it is necessary to classify it as an area where relatively new construction activities are restricted to prevent the old buildings from being demolished on a large scale.
Based on the above considerations, we reflect upon the areas from I to VIII with high visual sensitivity, according to the visibility analysis in the zoning Scenic Area: (1) The area with the highest visual sensitivity is the urban center where the Lingxiao Pagoda and Kaiyuan Pagoda are located (Areas III and IV). This area is close to the Scenic Area to be newly established for the Confucian Shrine of City and the Fengdong Stele. Thus, they are grouped together to propose one large Scenic Area. The area plays a key role in maintaining the historical urban landscape of the city center. (2) As the area from the Chengling Pagoda to the South Gate Tower via the Hua Pagoda is a visual highsensitivity area in the southern part of the old city, a single Scenic Area is proposed, including the southeastern part of the Chengling Pagoda (V), the southern part of the Hua Pagoda (VII), and the area between the two Pagodas (VI). The South Gate Tower has its separate Scenic Area as a PHS; therefore, it is not included in the evaluation of this Scenic Area of NHS, but it is suggested that the boundaries of the Scenic Area of NHS and PHS border each other. This area is crucial for maintaining the historical urban landscape of the southern part of the city.
(3) Since Longxing Temple has visual high-sensitivity areas (I and II) in both east and west of the temple, the Scenic Area shall be expanded in the east and west directions and presented in consideration of the current status of adjacent land parcels divided into large units.
(4) A visual high-sensitivity area (VIII) is located west of the Chengling Pagoda. Since the area is too far from the Chengling Pagoda, it is deemed impractical to designate and operate the area as the Scenic Area of the Chengling Pagoda.
In conclusion, we suggest the following Scenic Areas of seven NHS in Zhengding.
(1) The Scenic Areas of adjacent NHSs be grouped together to establish three large Scenic Areas, as shown in Figure 7(b). The Scenic Areas in the central part of the city are expanded from the existing 4.0 ha to 42.4 ha, from 4.3 ha to 24.5 ha in the southern part, and from 13.7 ha to 54.3 ha for Longxing Temple.
(2) Among these Scenic Areas, the southern parts of Longxing Temple and the Kaiyuan Temple, where the historical urban fabric remains, may be designated as "Scenic Area Type 1" and other parts as "Scenic Area Type 2." Restricted construction activities within the Scenic Area may be proposed according to the type of the area. Within Scenic Area Type 2, the construction of a project should not deform the historical features of the heritage site protected for its historical and cultural value (2017a). Additionally, is reasonable to limit the maximum height of the new building's roof and lowering it to less than 10 meters, which is the height of the traditional building's roof top and the height defined by the analysis criteria to preserve the historic city view. Within Scenic Area Type 1, detailed construction control requests for the volume, color, shape, and other aspects of new buildings need to be added along with the above restrictions.

Conclusions
Conflicts between the preservation of historical urban landscapes and the high-density development of cities are common in historical cities with high historical landscape value created by several high-rise architectural heritage sites. The Scenic Area is a legal method of protecting the historical setting around the cultural heritage, and through scientific zoning of the Scenic Area, zones for restricting construction and development can be created. This article rationally presents the Scenic Areas for the seven NHS in the old city of Zhengding County, China, using the method of analyzing visibility with ArcGIS, based on critically evaluating the existing Scenic Area.
In summary, five high-rise architectural heritage sites, including pagodas and towers, among the seven NHS sites served as objects of view or highlevel viewing points that created the city's historical skyline. Additionally, three high-level viewing points for tourists, located above the old City Wall, were added to analyze the visibility of the objects. The results revealed eight high-sensitivity areas in the high-rise architectural heritage sites, in addition to the expected areas of concern near the heritage sites. Generally, the Scenic Areas are zoned for each NHS; however, based on the above analysis, rather than individually zoning the Scenic Area surrounding individual NHS, we presented large connected areas by combining the spaces between NHS. Thus, the Scenic Area for the seven NHSs was largely divided into three areas: the central, southern, and Longxing Temple areas. Additionally, the Scenic Areas were divided in two types according to construction restrictions.
This article has the following significance. First, beyond the passive zoning of the Scenic Areas that only consider the individual value of NHS, the active zoning was produced considering the collective and landscape values it creates. This is based on the awareness of the specificity wherein various high-rise architectural heritage sites are concentrated.
Second, visibility analysis was used as a scientific method for the preservation of perceived landscape values. This article showed the case of detailed zoning of the Scenic Areas in dense areas, such as historical cities. Additionally, this method could be used to find the boundaries of areas through visual sensitivity of the terrain, as in the case of zoning Scenic Areas of cultural heritage in rural landscapes.
Third, we demonstrated the sustainability of the preservation of cultural heritage and urban development through rational zoning of the Scenic Area. The zoning of the Scenic Areas implies the determination of construction-restricted zones and the simultaneous construction possibilities of these areas. Therefore, this can help establish a long-term direction for urban development.
China is continuing her work on revising the Scenic Areas established in the 1980s to balance the effective protection of designated Heritage Sites and regional economic development. The values of cultural heritage sites and the circumstances of preservation are different from one another; thereby, the Scenic Areas should be planned according to those different values and circumstances. This study will aid in the rational zoning for sustainable conservation and development in the case of high-rise cultural heritage forming historical urban landscapes.