The City Axis, Beijing

Research on the city axis with Beijing as the main object URBAN MORPHOLOGY DOSSIER YANG XU

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Summary 1 The process of axis evolution 1.1 Conjecture of the origin of the axis 1.2 The evolution of the western city axis 1.3 The axis of ancient Chinese cities 1.4 Differences between Chinese and Western Axis 1.5 Types of urban axis

2 The process the central axis of Beijing 2.1 History of Beijing axis 2.2 Structure of space and culture of Beijing axis 2.3 Changes and development of Beijing axis 2.4

3

Morphology of different sections of modern Beijing city

Fractal city on the Beijing axis 3.1

Prototype in fractal city

3.2

What is a fractal cityďź&#x;

3.3

Hutong

4 Beijing Street Network Evolution 5 conclusion

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1 The process of axis evolution 1.1 Conjecture of the origin of the axis Whether in China or the West, typical axes appearing in human cities and settlements can be traced back to ancient times. In the existing research on the city axis, there are a series of conjectures about the inner reason of the origin of the city axis: In the existing research on the city axis, there are a series of conjectures about the inner reason of the origin of the city axis: (1) The imitation of the formal order in nature, especially the imitation of the basic and universal "symmetric" form in natural life.(figure 1) (2) Primitive humans without developed productivity have developed a yearning for order. Axial composition, a composition method with outstanding orderliness, has been seen in primitive art such as murals, totems, pottery, and sculpture. At the same time, it also influenced the creation practice of early human architecture, settlements and cities. (figure 2) (3) The widespread sun worship in early mankind may have made mankind the first to adopt east-west architectural layouts to cater to the rising and falling of the sun. However, the rule of north-south-oriented architecture found in life practice finally brought about the north-south orientation in the gregarious settlements. When the building has a common orientation, it will prompt people to connect the building and the narrow space in series according to their axis to form an overall order and group axis.

figure 2

figure 1

(schema 1)

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(4) As the "axis" of the composition form, and the "axis road" with traffic function, the sacrificial space in the center of the settlement is connected by a direct road to the gates at both ends, which can form the axis of the city; from the outer city gates To the palace, the "Royal Road", which demonstrates its ruling authority, can also form the axis of the city. The linear form of the axis composition is in line with the directness of traffic, and the graphic order constructed by the axis system also expresses the hierarchical distribution and layout of the space.

I think these conjectures about the urban axis, although difficult to verify, clearly suggest that the urban axis should not be driven by a single power to produce its prototype. The axis has linear morphological characteristics, clear geometric order characteristics, and directionality compatible with the orientation of livable buildings. It is also convenient to combine with practical functions such as traffic route organization and primary and secondary spatial layout. There is not only a perceptual artistic understanding, but also a foothold on a practical level. Like many art forms, axis design must have a process in history from unawareness and consciousness, from prototype to perfection, from the gradual formation of conscious design techniques to its continued development, perfection, differentiation and sublation.

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1.2 The evolution of the western city axis The Acropolis of Athens in ancient Greece used the main pilgrimage road as the basis for the organization of the city's spatial factors. Although the pilgrimage road is not a straight line, the geometric form of central axis symmetry in the Acropolis only exists in the single building non-building groups such as the Acropolis Gate and Parthenon Temple. It seems that the Acropolis is a free layout, but it is also It embodies the role of the axis of establishing connections and organizing layout with linear clues.

Acropolis site-plan

In the ancient Greek period, Hippodamus used regular, homogeneous, geometric grids in the planning and construction of cities such as Miletus . Although this form of planning was not pioneered by Hippodamus, it has been practiced in the ancient Egyptian city of Kahun and some ancient Indian cities, but it was the first theoretical exposition by him and was later used in the reconstruction of the city after the war.

Large-scale practice has become a classic paradigm that ancient Greek cities can follow. This paradigm city follows the philosophy of ancient Greece, advocating a strong geometrical, balanced, and harmonious spatial order, and the road network structure in the form of a square grid also presents clear linear characteristics. These cities cannot be considered to be characterized by axis lines but they have distinct geometrical orders and linear clues.

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Although the above examples all show the linear characteristics of early urban. But not necessarily the axis. However, Ancient Western cities did have very typical urban axes. For example, Alexandria in the Greek period had a relatively complete grid with an orthogonal layout. The two widest streets form the main axis of the city. The main axis which connects temples, gymnasiums, cemeteries etc. And there are several (may be called secondary axis) streets perpendicular to the main axis one of which end with important public buildings and intersect the main axis with a square.

This is a typical early western axis, with geometric aesthetics, and also played a role in organizing important public spaces in cities.

During the Renaissance, influenced by《de Architectura》 of Vitruvius the development of the urban axis was promoted. The architects proposed a variety of ideal city models (pic 4). At this time, the urban planning already has obvious axis characteristics.

Until the 18th century, in France, the city of Paris hosted by Haussmann was transformed into the most typical case of the western city axis. Paris

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has established a large-scale linear and radial road axis system, obtained a combination of primary and secondary axis groups and urban landscapes, and also conveniently and effectively controlled the city's territory. The main axis of the city extends from the existing axis of the Tuileries Garden with a total length of about three kilometers with the Louvre and the Arc de Triomphe as its two ends respectively and the Tuileries Garden and a circular square are connected in the middle. In the 1950s, the increasing demand for office buildings in Paris prompted the government to make a decision to expand the urban area of Paris and build a central business district. The historical axis from the Louvre to the Arc de Triomphe continued to extend westward to reach the newly opened la defense.

At the end of the 18th century, a 3.5-kilometer east-west axis and a shorter north-south axis were planned in the downtown area of Washington, USA. A series of public buildings are set on both sides of the axis. The Washington Monument towering at the intersection of the two axes is a proper and necessary positioning and separation of this group of orthogonal axes. In order to ensure the unified coordination and priority distinction of important buildings in the central district government, the height of other buildings shall not exceed 33.5 meters ( height of the Capitol).

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The new capital of Brazil, Brasilia, planned and designed in the middle of the 20th century, the urban spatial framework consists of two axes with different functions intersecting east-west and north-south. The plane is symmetrical in the shape of an airplane. The city is like a large totem symbolizing the rise of the country. The Brasilia axis is almost entirely based on the CIAM principle represented by Le Corbusier as the capital designed and constructed. It has the ultimate form of modernist cities and architecture.

The 8 km long east-west main axis is shaped like a fuselage, and the space control range of the national power core is only at the east end of the east-west main axis; the 13 km long north-south secondary axis is contrary to the usual straight line form, which is curved. The wing shape conforms to the order of the natural environment. The functions on both sides of the axis are mainly commercial, residential, and embassies.

The planning and construction of Brasilia has been praised for its upright and majestic form, and it has also been criticized as a typical case of formoriented, lack of consideration of economy, society and traditional culture.

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1.3 The axis of ancient Chinese cities China has taken the city’s physical axis as the most fundamental reference mark of the city to serve politics and reflect the historical origin of traditional ethics and morality. In the primitive society of China, the rudiment of the organization of architectural groups in the form of axis symmetry has already existed. In the capitals of the Xia and Shang dynasties (c.2070c.1046BC), the central axis layout of the same degree has appeared.

The theoretical explanation of the axis can be traced back to《Kaogong ji 》 which more comprehensively demonstrated the urban construction paradigm of the Zhou Dynasty（1050-771BC）: “匠人营国，方九里，旁三 门，国中九经九纬， 经涂九轨，左祖右社，前朝后市，市朝一夫” Translated into English, the rules for building a capital city recorded in 《Kaogong ji》are: the outline of the capital city is rectangular, with walls on each side, and the walls surrounding the city have nine LI (4.5km) on each side and three gates on each wall. There are nine north-south avenues and nine east-west avenues in the capital. Each avenue can accommodate nine carriages in parallel, in order to demonstrate the imperial majesty.

In the layout of the city, there is an ancestral temple on the left, and residential buildings on the right, facing the market. The front is the power and political center, and the rear is the bazaar facing a large area of farmland.

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The Eight Diagrams (bagua) used in it are very similar to the Western ideal city

The feudal culture and hierarchical order in ancient China embodies the social structure of the supremacy of monarchy and the inferiority and order which is completely different from the independent spirit of individual in the West.

Confucianism established its dominance in a solid feudal society after the Eastern Han Dynasty (202 BC–220 AD). In the course of the evolution of Chinese cities in the past two thousand years, the central axis has gradually matured in urban construction, especially in capital construction.

The common features of these typical central axis cities include: royal palace is in the center, the north-south central axis of palace extends as the main axis of the capital, and the shape extends from the north to the south.

In addition to the main shaft, there are some parallel secondary shafts to contrast and strengthen the main shaft. With the gradual formation of the "宫-城-郭"（royal palace-imperial city-City wall）multiple loop mode, the level of axis design also gradually emerged.

The urban structure of China is both nested and rhythmic alternating between Yin and Yang and they are complementary also, The city wall provides a focus on the central space. It is not difficult to find that ancient

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Greek temples are also a kind of spatial nesting with rectangles as the matrix.

Although they express different spirits and cultures.

The above characteristics began to be manifested in the Luoyang(493– 534) (the capital city of the Northern Wei Dynasty 386-584)

In the Tang Dynasty, Chang'an had the characteristics of grand scale, clear divisions, and neat neighborhoods. The layout of streets and houses complies with the principle of fractal city,This part will be discussed in detail in the chapter of fractal city.

The axis connecting the gates of palace and the outer palace gates in city forms the main axis of the city. Under the command and organization

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of this axis. The palace, city and outer city are arranged separately, and the entire layout is symmetrical and rigorous, solemn and thin, demonstrating the supreme imperial power status. Through the axis extending from north to south, the space of Chang'an City is arranged in an orderly manner, becoming a model of traditional Chinese urban spatial structure. then gradually matured until the Dadu (the capital of Yuan Dynasty) formed a complete set of systems, and finally reached its extreme in Beijing during the Ming and Qing Dynasties.

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1.4 Differences between Chinese and Western Axis American urban planner Edmund N. Bacon once discussed the difference in visual experience between the Washington axis and the Beijing central axis: "If a person stands at the foot of the Washington Monument (at the intersection of Washington's main axes), he only needs to circle its base and move only a few feet, you can appreciate all the elements of the main design of Washington. but In Beijing, unless you move through the space of a two-mile passage, you cannot appreciate its design."

According to Bacon’s point of view, most urban axes in the West adopt an organization method that uses open space as a hub and parallel axis buildings on both sides. The traditional axis of Chinese cities has its own characteristics. It adopts the form that the palace sits on the axis and occupies an important position in the center. The common symmetrical axis of the palace is combined with the city's royal road space (composed of city walls and gates) to form a city. The central axis sequence. The intervention of the volume of the palace on the axis hinders the penetration of human vision and movement on the axis. This makes it clear that although the axis of Chinese and Western cities can be clearly identified from a “bird’s-eye” view or 2D plan, the axis of Chinese cities cannot Achieve a clear view of the entire axis from the perspective of people. At the same time, China's urban axis also presents the characteristics of being centered, fixed at both ends, unique main subject, and north-south direction. This is in great contrast with the variability of the western city axis, which can extend radially in many directions, does not necessarily have a single subject, and follows the direction of spatial movement rather than geographic orientation.

From a historical point of view, this obviously shows the more distinctive symbolic significance of absolute imperial power on the Chinese axis.It shows that the ancient Chinese axis emphasizes the realization of itself and serves as a tool to highlight the extraordinary status of the palace architecture, while the western axis plays a more important role in

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organizing the framework and basis of space and architecture in the city as a whole. Rich in the spirit of democracy and freedom.In the whole history, human beings transform space and make it a reflection of power relations in human society in the material world, which constitutes a medium for instilling ideology and values for people. This reminds me of the collective memory and collective consciousness in psychology. Later, in modernism, Aldo rossi especially emphasized the "time" of architecture: without history and background, architecture is just an ordinary house, and history makes it a carrier of thoughts and emotions.In certain periods, they have also become a tool for the ruling class to symbolize, deify, and declare its power.

In particular, the axis, as a large-scale public space order, is generally formed under the strong control of the state. The comparison between the Chinese and Western axes requires a deeper cultural and political contrast to find the underlying reasons.

Chinese traditional culture, its feudalism has not undergone essential changes during its thousands of years of inheritance and development.

Therefore, the central axis pattern of the imperial power supremacy thought was continued, and the continuous improvement along with the development of productivity reached its extreme in the late period of feudal society from the Ming and Qing Dynasty to Beijing.

And Western culture is different from Chinese culture. It is developed by the civilization centers of different periods and different places, influencing and complementing each other. This has created its pluralistic and democratic characteristics. Therefore, Western cities embody the characteristics of this pluralistic democracy instead of a unity of thought.

The development of the axis system embodies the “right here and right now� culture in different periods and different regions. Among them, the absolute monarchy period is similar to Chinese feudal imperial power, but in general it is very different from Eastern culture. The civic cultural tradition that continues to this day has created the phenomenon that there is no absolute

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subject on the western axis. The axis is mainly composed of traffic corridors and open spaces.

1.5 Types of urban axis (1) Classification of composition levels It can be divided into global axis and local axis. They have different components in the urban composition, and the overall axis runs through most of the city in at least one direction. Part of the axis plays the role of a local area of the city rather than the overall axis of the whole area or acts as a monumental public space in the city center.

(2) Formation method Can be divided into overall design axis and self-improvement axis The overall design axis is generally the axis of a newly built city, such as the city axis of Washington and Brasilia; the self-improvement axis is a city that has not been fully planned or only planned an existing part of the current axis in its history. , Such as the city axis of Changan, Beijing, and Paris.

(3) Function It can be divided into development axis, landscape axis and function axis.

The development axis controls the direction of urban structure expansion and the direction of urban function transfer, and most of them have obvious important traffic linearity; the landscape axis plays a dominant role in the urban landscape system, connecting and organizing the main urban landscape nodes;The functional axis concentrates similar or related urban functions in a linear area.The city axis sometimes combines the abovementioned multiple types (4) Property The specific nature can be divided into political axis, economic axis, traffic axis and greening axis. The political axis is mostly seen in national capitals and is a monument to show the spirit of the country. Therefore, it is often difficult to balance practical functions and cause certain problems;

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The economic axis is a collection of economic advantages formed under complex factors and has a strong radiating effect;Traffic axis refers to the city axis with the embodiment of traffic function as the primary feature of the axis; the green axis is the linear concentrated area of urban green space and ecological protection area, which usually reflects the main landscape and image of the city.

(5) morphology

The Paris Axis as an example Major and minor axis

cross axis

radial axis

Multi-axis juxtaposition

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The Barcelona Axis as an example

Although from a morphological point of view, the distribution of streets in Barcelona has a grid characteristic.

However, the urban axis dominated by Gran Via does not have an obvious grid axis, but has the characteristics of parallel axis, Major and minor axis. It is worth mentioning that Gran Via is the main axis road in Barcelona, with a total length of 13.1 kilometers, extending parallel to the coast to the southwest and northeast. It passes through the three most important squares of Barcelona and also intersects all the city axes in Barcelona city.

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2.1 History of Beijing Central Axis It is often said in Chinese philosophy, the cosmological view of "harmony between man and nature ", the view of nature of “ Harmonization of object and ego " and the view of environment of "yin and yang ". As mentioned in the previous chapter, the historical and cultural and philosophical reasons for the formation of the traditional urban axis, In this chapter, I will specifically study the process of last ancient capital with central axis characteristics in ancient Bejing. At the same time, l will also analyze the new development of urban axis in modern society.

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2.1.1 period of the formation central axis The construction of the Dadu is an example of the strictest adherence to the《Kaogong ji》 in the capitals of all dynasties. The topography of the city is flat and the palace is located in the center.

Taimiao (the ancestral shrine) is set to the east, and Shejitan(a Confucian altar) is set to the west. The road system in the city forms a square network structure. each level of (palace, imperial city, capital city) each level has walls. There are 11 gates on the outermost side, three on each of the east, west and south sides, and two on the north side. The city gates are arranged symmetrically with the main roads in the city, and east-west hutongs are connected in series. The pattern of city gates(图) as the elements of the Yuan Dynasty established the original centripetal city pattern and city axis. Government institutions were established on the east and west sides of the central axis of the imperial city, and the central axis of Beijing was extended to 4.8 km.

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2.1.2 period of the perfection of the central axis In 1368, the Ming Dynasty transformed the city of Beijing. As the northern part of the Dadu is empty and far away from the palace, in order to resist the invasion of the remaining Yuan dynasty soldiers, Ming Emperor Zhu Di abandoned the desolate area to the north and built a new city wall on the line of Desheng men (Gate Desheng) and Anding men Gate Anding.(

)

In order to broaden the front space, the emperor pushed the southern city wall of the Yuan Dynasty from today's Chang'an Street( south to Gate Zhengyang(today is called qianmen).(

) to the ) During the

Jiajing period of the Ming Dynasty, the Central Plains area was repeatedly invaded by the north. In order to resist the invading enemy, it expanded to the south to surround the Tiantan(an imperial complex of religious buildings), Xiannongtan (Altar of agriculture ), and the central axis of dense residential areas to Gate Yongding, forming a " 凸 " Chinese character shape. At this period, the traditional central axis of 7.8km from south to north is gradually improved, and today the plane pattern and urban spatial form of Beijing’s old city have basically taken shape.

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plan de noli(1817)

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2.3.1 Structure of space and culture of Beijing axis The central axis of Beijing is like a symphony with many changes, with overtures, climaxes, and endings.

The southern section is the "Overture" of the symphony, which is mainly composed of Yongdingmen, Tianqiao, Tiantan, Xiannongtan, and Zhengyangmen Street.

The middle section is the "climax" of music, including Zhengyangmen, Qipan Street, Palace Square, Tian’anmen and Duanmen, Taimiao, Shejitan, Forbidden City, Jingshan, and Di'anmen. There is no doubt that the Forbidden City is the climax of the highest .

The northern section is the "end" of the symhony, with Di'anmen Street and Bell Tower and Drum Tower as the main content.

The spatial structure can be divided into 12 units. These spatial units have different north-south length, east-west width, and upper and lower heights, which are continuous but relatively independent. According to the space classification of cultural types, it can be divided into four categories: (1) imperial power political space (2) security defense space (3) sacrificial space (4) resident and commercial space.

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12.gulou/zhonglou

11.unit jinshan 10.unit Forbidden city 9.unit shejitan 8.unit tai miao 7.unit tian’an men 6.unit palace square

5.unit zhengyangmen 4. unit xiantannong 3. unit Tiantan 2. unit tianqiao

1. unit yongding men

（today is called qianmen）

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Unit Tiantan: Tiantan (The Temple of Heaven) is a place where the emperors of the Ming and Qing Dynasties "sacrifice to the sky" and "pray for the valley", located on the east side of Zhengyangmen. The altar area is round in the north and square in the south, meaning "The sky is round while the ground is flat". Surrounded by two walls, the whole altar is divided into two parts, the inner altar and the outer altar.

The total area is 273 hectares. The main buildings are concentrated in the inner altar.

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Unit zhengyangmen and square : Zhengyangmen, the southern gate of the capital city, is the tallest among the gates of Beijing. Every winter solstice, the emperor goes through Zhengyangmen and Xiannongtan Tiantan on Zhengyangmen Streetďźˆqianmen street today to worship. .

Zhengyang

The "T"-shaped square built in the Ming Dynasty starts from zhonghuamen in the south and tian'an men in the north. The square is surrounded by palace walls. On the north-south vertical axis, there are wide imperial roads. The north-west extension has Chang'an Street at both ends.

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Unit forbidden city

F r o m G t r h o e m p t e h rs e p p e e ct The Forbidden City was the imperial palace of the Ming and Qing rs iv dynasties. It was also the center of theep "nesting box" of the palace, imperial e city, inner city and outer city. The oct Forbidden City (pronounced zijin in f iv Chinese) is a metaphor for the imperial s palace in ancient astrology and the e "ziwei" in Ching. They believe that thepo Forbidden City is not only the origin a of Beijing's central axis, but also the cfcenter of gravity on the ground. The s e south. The central axis buildings of Forbidden City reflects the north facing p p a are the Meridian Gate, the Gate of the Forbidden City from south to north la c Supreme Harmony, the Three Hallsn of the Front Dynasty (the Hall of e ni Supreme Harmony, the Hall of Zhonghe, p and the Hall of Baohe), the Gate n la of Qianqing, and the Three Palacesg, of the Inner Court (the Palace of n b Qianqing, Jiaotai) Hall, Kunning Palace), Kunning Gate, Imperial Garden, ni o n t Shenwu Gate. g, h b t o h t e h s

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Surrounded by the annex buildings on the east and west sides, the building on the central axis of the Forbidden City is like a winding dragon, undulating high and low, and can be retracted freely.

Among them, the Meridian Gate is the southern gate of the Forbidden City and the tallest building in the Forbidden City. The tower is built on the city platform, like a rising dragon head, showing deterrence and defensive functions. The three main halls of the outer dynasty and the third palace of the inner court are all saddles.

The undulating height changes in an orderly manner from high to low, and then from low to high. The line in the middle of the roof is like a dragon body undulating north-south through the Forbidden City; while the Qin'an Temple and Shenwumen exit in the Imperial Garden in the north, The line in the middle of the roof becomes smooth again, like a stretched dragon's tail.The dragon was a symbol of the emperor in ancient times, and the facade of the central axis of the Forbidden City is like a dragon in the architectural planning.

Not only that, the ancient craftsmen intertwined these buildings through the contradictory methods of big and small, wide and narrow, high and low, complex and simple, etc., forming a diversified unity; from the guidance of the subtle, it gradually changed to The majestic subject, then to the magnificent peak, and finally to the euphemistic closure, giving people a visual ups and downs.

From the perspective of space planning, both the south of the Hall of Supreme Harmony(G) and the north of Kunning Palace(F) are enclosed by the door to the door and the corridors on both sides. Through the connection and penetration of the doors, each seemingly closed space is closed. Stranded into a large flowing space.

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Court audience given by Emperor Qianlong, Forbidden City, Hall of Supreme Harmony

The six palaces between the Hall of Supreme Harmony and the Kunning Palace form a relatively independent space. They are places for the emperor to govern and the empress’s activities. They have a certain degree of secrecy. They can only be reached from both sides through numerous thresholds and steps.

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2.1.3 new development of the central axis in modern city

1

2 A

6 A

3 A

4 A

5

After the founding of the People's Republic of China in 1949, cities were no longer tools of imperial power to rule. This fundamental change brought about qualitative changes in the construction and development of cities. With the accelerated pace of modern industrialization and modernization, the scale of cities has expanded, the population has increased sharply and a series of changes such as changes in lifestyles and transportation methods have brought a strong impact on the original urban operating system. The specific performance is:

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Part of the city walls on the central axis of (1)Di'an men(2)Xi’an men(3)west changan men(4)east chang ‘ an men (5) Zhonghua men (6)dong‘an men (7)yongdingmen etc were demolished. In this way, the basic spatial model established by the city gate and wall was partially broken.

Although the overall morophology and structure have been maintained, the cultural connotation and use functions of the central axis and its various spatial units have undergone tremendous changes.

Temple of Heaven Unit: It is now the Temple of Heaven Park. With the overthrow of the feudal monarchy, the Temple of Heaven lost its status as a space for sacrificial rituals. It was changed to a park in 1918, and its nature and functions have undergone tremendous changes.

Tiananmen Square Unit: After the Revolution of 1911, the closed state of Tiananmen Square was broken, and the traffic between the east and the west was connected. The Great Hall of the People, the History Museum, the Monument to the People's Heroes, the Chairman Mao Memorial Hall and

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other large public buildings. Its nature thus transformed into a very largescale People's place.

With the continuous expansion of Beijing's urban scale, the central axis was split by many urban arterial roads. The original Beijing central axis was no longer tall and majestic, but was submerged by high-rise buildings rising from the ground on both sides of the central axis.

However, with the 2008 Beijing Olympics, the construction of Beijing's central axis has been brought up again: the spatial sequence of the city's central axis extending from north to south has reconstructed the urban pattern of Beijing with a scale of nearly 30 km.

Morphology of different sections of modern Beijing city (1 )From Tianqiao to Zhengyang Gate was once the most active section of the entire axis, this area retains a large number of traditional courtyard residential hutong area, but also as the old city in the transformation of the key protection of the cultural essence of the district and historical district （ 2）Tiananmen Square is the focus of the entire modern axis space sequence, as a symbol of the national political center.(3) From Tian’anmen to Jingshan Park, the magnificent Forbidden City is the essence of the traditional central axis is now an important cultural heritage(4) From Jingshan Park north to the zhong lou mainly for the city well area. (5) From the zhonglou to the north, the traditional space breaks, gathered a large number of office industries and residential living areas.

Relying on the flexible layout of water body form, urban planning and fish bone-like hutong structure in the old city interspersed with it, forming the unique texture characteristics of Beijing. The texture of the focused areas on the modern central axis above can be seen by plan positif.

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(6)e

(5)e

(4)d

(3)c

V

(2)b

(1)a

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Focal area in Different sections(2.25km2) of the modern Beijing axis

(6)f

(5)e

(4)d

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(3)c

(2)b

(1)a

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From the comparison of the morphology of the 6 sections on the central axis, it can be seen that the closer to the city center, the stricter and finer the urban texture; the closer to the outer area, the more relaxed the urban texture. Taking into account the different sequence of construction time, this change also reflects from the side the change of the planning and construction of the central axis in different periods.

(6) Starting from the disorderly residential area at the southern end of the city, along the central axis to the north, the layout of buildings on both sides of the road is becoming denser and symmetrical.

(5) The scale and rhythm of the spatial layout on the central axis of the Yongdingmen and Qianmen Street sections have gradually increased, and the scale of the Tiananmen Square section to the center has suddenly enlarged.

(3) (4) The ancient central axis sequence space, which is suitable for walking, preserved from the north of Tiananmen Square to the Bell and Drum Tower.

(1) Going all the way to the north, the high-rise commercial office buildings present the spatial characteristics of modern Beijing.

Until the central axis of the Olympic Park ends in Yangshan.

This series of changes in the rhythm of urban space from south to north shows the pattern and temperament of Beijing.

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3 Fractal city on the Beijing axis 3.1 Prototype in fractal city The word fractal was proposed in the paper 《How Long Is the Coast of Britain，Statistical Self-Similarity and Fractional Dimension》published by Benoît B. Mandelbrot in 1967. The original meaning is irregular and fragmented. It is a fractal of nature The unified characteristics of —— selfsimilar structures such as snowflakes, lightning, trees and various vegetables like broccoli.

Graphics with fractal characteristics are usually geometric objects that are self-similar and can be generated through iteration. That is, in a certain form, the shape of a part is similar to the whole, and the self-similarity here can be the same or the prototype.

The cycles and repeated changes of fractal iterations can generate rich and infinitely fine structures.

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3.2 fractal city A graph that can strictly satisfy the self-similar condition is called a regular fractal.

But this kind of regular fractal is only a small number, and most of the fractals are irregular fractals in the statistical sense. We call them random fractals, or statistical fractals.

The above is the interpretation of fractal geometry through mathematical logic. Even though this is a study of modern mathematics, we find a similar logical structure in the Chinese I Ching Bagua Diagram.

The graphics after the first iteration of cantor set fractal() is the same as the Chinese Bagua

Diagrams().

Also in Chinese garden architecture, fractal method is particularly prominent 1559(Ming dynasty) in shanghai china Yuyuan Garden

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In fractal graphics I mentioned the self-similarity with the prototype or subject. "Prototype" can be simply understood as the initial reference.

Prototype is the original type of living space model, which most directly expresses the function of living space and the spirit of the place.

The Italian architect Aldo Rossi who has made a big breakthrough in prototype theory. Rossi believes that “all architecture comes from a limited number of forms created by ancient people, and these forms have been recognized by humans and certain races, and have entered people’s collective memory (the collective memory I mentioned in the previous chapter)"he believes that the task of the architect is to find the archetypes that exist in people's collective memory, and to excavate the eternal value in this archetype to reflect "eternal human life".

Giorgio Grassi puts more emphasis on the influence of collective memory on architectural forms. In his opinion, only when the society and the collective think it is reasonable, the architectural form can become something that looks reasonable. In addition, Louis Kahn, his architecture pays great attention to the prototype (the rustic essence of form). His architecture has a very strong spirit of place, which makes you very aware of it, and it seems to hide a certain vitality.

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I will not go into details about the development and reason of architectural typology and prototype. But what I want to emphasize is that the exploration of architectural prototypes is the basis for the exploration of fractal cities, which is far more complicated than the fractal geometry produced by multiple iterations of a geometric figure. <a city is not a tree>proposed by Christopher Alexander. Because from the structural point of view, in the structure of the tree, there is no single leaf growing on this branch and another branch, unless the trunk connects them as a whole. But the relationship between the elements in the city is not only a hierarchy(b).

When we think in the tree mode, we actually use simplicity to replace the complex cross-relationships between living people and cities(a).

So when we talk about the city of fractal, we only study the geometric relationship between the prototype and the whole from a plane perspective.

So the theory of fractal city is mereology. â&#x20AC;&#x153;mereology is the theory of parthood relations :of the relations of part to whole and the relations of part to part within a wholeâ&#x20AC;? by Christopher Alexander

However, we can better summarize the composition of ancient Chinese fractal cities from the definition of building types and prototypes in Western architecture.

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Changâ&#x20AC;&#x2122;an The regular modular fractal grid

The overall structure of Chang 'an City follows the distribution rules of the power law. From the first level to the next level, the reduction coefficient changes from 1/2 to 1/3. Such an iterative decreasing law alternates with the changes in the I Ching

The 16 districts within the city wall are separated by two east-west and north-south avenues. The law of fractal power can get the internal roads of 135m, 45m, 15m, and 2m. This subdivision structure makes it possible to combine high-density and loose-structured buildings, even including courtyards of different scales. For Chang'an, which had a high-density population at the time, although it seemed to require a strict layout, it actually allowed flexible changes in the boundaries between urban and rural areas. This makes the high-density grid not completely filled, so crops can be planted in the center. Chang'an is really a dense and green city.

It is very inspiring for the contemporary sustainable high-density cities which we look forward to.

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Just like Chang'an. Beijing was also a tree-lined city. The neighbods connected by alleys formed a huge chessboard network. siheyuan, a house with square courtyards, is the prototype of traditional Chinese fractal urban layout structure. 四合院（siheyuan）“四”The number 4 in English means four directions （east,south,west,north）"合" refers to houses surrounded by four sides 院 means courtyard which is formed by the four sides.

This is the most basic and typical, and it derived one entre, two entre, three entre, etc. siheyuan

.

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hutongs are alleys formed by lines of siheyuan. As far as traditional cities are concerned, the urban texture is an important part of the historic urban landscape, and he established an important connection between the study of urban form and residential form. In Beijing old city, Hutong plays such an important role.

The streets and hutong of Beijing are generally arranged symmetrically on both sides of it.

Although the texture of the hutongs in most areas is already messy, the organizational relationship between the hutongs and the central axis can still be partially reflected.

It can be seen that Hutong is closely related to the central axis and together form the skeleton of Beijing City.

Schematic diagram of the evolution of hutong

Yuan dynasty

Qing dynasty

today

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The hutongs in the old city of Beijing are diverse and numerous.

The specific number of Beijing hutongs has changed with historical changes.

The following table is the statistical data on the number of hutongs in Beijing since the Yuan Dynasty. It can be seen that the largest number of hutongs was in the early 1990s and has been declining since then.

According to ă&#x20AC;&#x160;zhouliă&#x20AC;&#x2039; records, two carriages can be accommodated in parallel with sidewalks on both sides of the road. The width of the alley should be about 7-9 meters. It can be seen that in the Yuan Dynasty, the width of the hutong was six steps(9m), and those wider than it were called main streets or small streets. This rule was no longer so strict in the Ming and Qing Dynasties, so that some places appeared irregular alleys, wide or narrow, straight or diagonal.

Statistics of the width of Hutongs 2015

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Statistics of the length of Hutongs 2015

Both sides of the hutong are basically single-story buildings. After the Ming and Qing Dynasties, it was basically a courtyard house. The height of the street elevation is generally about 3 meters, and the width of the hutong is generally 3 meters to 6 meters. If it is 6 meters, the ratio between the two is 2: 1; if it is 3 meters, the ratio between the two is 1ďź&#x161;1.

When the spatial scale of the road, mainly the aspect ratio, is between 1:1 and 2:1, the space of the road maintains a balanced state. Pedestrians are on one side of the road, his vision can cover the entire building, and will produce a proper sense of enclosure. This is one reason why most hutongs in Beijing give people a cordial feeling. Beyond this limit, the sense of aggregation and deepness in the hutongs will be strengthened, creating a sense of visual and psychological oppression.

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Beijing Street Network Evolution Because the purpose of my thesis is to study the city axis with Beijing as the core. Therefore, the research on urban streets will not focus on a single street. The main purpose is to study the changes in the street network connected to the Beijing axis. The research method used here is the basic space syntax which l learned by myself.

In the context of spatial syntax, each street segment has two meanings: （1）the starting point and ending point of travel; （2）the only way to travel ， which derives two classical syntax parameters:(Integration)and (Choice)； (Integration) is used to measure the distance from any street segment to other street segments in the system, and can also be regarded as topological reachability;(choice) is used to measure the probability of any street segment in the system being crossed by the shortest topological distance path of the other two street segments. A space with a higher degree of choice is more likely to be passed by people.

Bill Hillier classified different street segments into foreground network and background network according to the degree of integration and degree of travel, and believed that the average and maximum value of degree of integration and travel could represent some structural characteristics of the street network system. Bill Hillier classifies different street segments into foreground network and background network according to the degree of integration and travel, and believes that the average and maximum values of (Integration) and (choice) can represent some structural characteristics of the street network system.

Fore ground network: The street sections with the top 20% in terms of integration degree or travel degree carry more functional distribution and economic activities. Among them, the top 5% of the street sections are the integration/choice core, which is the core axis of urban politics, economy and culture. background network: The integration or choice value ranks in the bottom 80% of the street segments, which are mainly used to provide places for residents' daily life and residence.

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Core integration

Fore ground Back ground

According to carte in 1912, the imperial city occupies the geometric center of the old city in absolute isolation. There are two highly accessible square rings, namely the inner ring (second ring) surrounding the imperial city and the outer ring formed by the streets that pass through Dongcheng District and Xicheng district such as Dong dan avenue and Xi dan avenue. Several streets such as Qianmen Street and Xuanwu men Street connect the inner and outer cities.

According to the 1928 map, the accessibility of the imperial city was improved along with the opening of the city wall, and several streets, such as North-south Long Street and Cianchi Street, entered the foreground network. Construction activities such as the expansion of Tian 'anmen Square and the extension of Chang 'an Street resulted in the replacement of the inner city's double square ring with a concave integrated core structure. A number of high accessibility street sections are located in Dongdan Street, Xidan Street and Chang 'an Street and meet along the road.

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1928-1949, the original core axisymmetric integration in west by obviously, this is clearly benefited from the first through the north-south strip of the old town, it consists of xidan street, xuanwu gate street, not only has the highest degree of consolidation, many connected to the road of accessibility also get a boost, accordingly, west side at that time speeding up development speed, xidan is become one of the most prosperous commercial center.

From 1949 to 1976, the East-west Chang 'an street became the most accessible road and was an important cultural and political venue. It is also a veritable new central axis, highlighting the ability of political forces in socialist countries to shape ceremonial Spaces. At the same time, the disequilibrium pattern of the integrated core still exists, but the tilt direction is contrary to that of the previous period. The staggered long street system in the east constitutes a new integrated core cluster area, which is related to the connection of Chang 'an Street and the more perfect network structure outside the second ring road in the northeast.

From 1976 to 1992, the foreground network north of Chang 'an street formed a good symbiotic relationship, which led to a multiplier effect of integration. To the south of Chang 'an street, not only the overall accessibility is low, but also the associated street segments are mostly background network, which leads to the double reduction effect of the degree of integration.

From 1992 to 2016, the continuous implementation of large-scale renovation led to a sharp reduction in the number of old city street sections from 10,925 to 9,670, resulting in a significant adjustment of the integrated structure. First of all, the accessibility of the South 2nd Ring increased significantly with the density and improvement of the street network to the south of Chang 'an Street, and organically connected to the North 2nd Ring.

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Second, the whole 2nd Ring and a number of long streets running through the old city together form the "Ring + grid" type integration core, along which not only include Tian 'an men Square, Zhongnanhai and other national power centers; The Forbidden City, temple of Heaven.

And other world cultural heritage sites; It also includes financial street, Wangfujing and other financial and commercial centers. At the same time, the regular grid structure formed by Dongdan Street and its series of vertical and horizontal hutongs, as a legacy of the Dadu Period of The Yuan Dynasty, still maintains its remarkable access advantage, and gradually transforms to a creative cultural block on the basis of resident culture. In contrast, the accessibility of many traditional hutongs and alleys in other regions has been greatly reduced, and there is also a significant decline in real life.

Year

The street section number

Maximum

Average

Integration Integration

Maximum

Average

Integration/

choice

choice

Choice R3

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conclusion Kevin Lynch pointed out in ă&#x20AC;&#x160;The Image of the Cityă&#x20AC;&#x2039;: "For any particular city, there seems to be a public image, which is a common part of many individual impressions. There may also be a series of public images, each of which represents

with a large number of urban residents".

The role of the axis and the significance of its own existence are obvious. Many outstanding urban planning and design in ancient and modern China and abroad are inseparable from the existence of the city axis. It is precisely because of the existence and use of the city axis that not only has it created each city. The unique urban landscape form creates a unique urban image. And it provides the most important and rich reference for our urban planning and construction today.

The central axis of Beijing, as a representative urban space that concentrates the temperament of Beijing, develops a magnificent urban spatial order pattern at the stage of formation, improvement and extension.

The beauty of the central axis is the result of the joint action of multiple dimensions, not only because it connects urban Spaces of different types and periods, but also because of its inclusiveness and openness and its vitality of self-renewal in the inheritance and continuation of urban traditions.

To discuss Beijing's temperament in the context of architecture, we need to analyze its current situation and inquire into the collective tendency of local architectural practice that influences Beijing's urban construction behind the phenomenon. It is the law, the thought and the image hidden behind the appearance, influencing all the new things in this city. Reflected in the urban space of the central axis, this temperament is moderation, balance, founder, atmosphere, but also confrontation, derivative, ups and downs.