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Study of the Inherent Causes of Formation of Settlements Based on Satellite Map Observation

According to legend, there are several settlements in the form of “Bagua” (also called the Eight Diagrams) in Guangdong Province of China. For a long time, the public propaganda and some scholars all consider that the construction of this type of settlement is an imitation of gossip, so-called Bagua of Tai Chi. Using satellite map observation technology, this study defined the preliminary concept of the settlements in the form of Bagua, collected the statistics of the quan-tity and location of these settlements, and gathered a description of the distribution and overall plane graph of them. Through graphic analysis and isomorphism method, it is found that iso-morphic relation exists in many ways between the distribution region of those settlements and their surrounding geographical environment. From our viewpoint, the form of Bagua is only the external appearance of the settlements, and there are more important inherent causes of formation for them. First of all it is the defense of floods, followed by the defense of human disasters, and last but not least it is the adaption to the forms of social organization. The formation of the settlements in the form of Bagua had an ap-parent cause of defending the natural and human disasters, and it adapted the forms of social or-ganization. Then in the development of these settlements, the influences of the Bagua of Tai Chi as well as feng shui are integrated. In nature, the purpose of settlement form is to create optimal living environment.


Introduction
As a place of strategic importance in Xijiang River basin, Gaoyao Region in Guangdong Province is a geo-graphical hub of Guangdong and Guangxi, and the convergence of ancient civilizations. It is said that in Gaoyao Region there are several settlements in the Form of Bagua, including Xiangang Town (Fig.1), Licha Village, Baizhang Village and Shangkong Village, etc. This settlement pattern is significantly different from other types of settlements in Guangdong. For a long time, Licha Village and Xiangang Town, etc are commonly known as "Gaoyao Bagua Villages". Some scholars, as well as in the official publicity materials, hold that these settlements are created based on the concept deriving from the Taoist Tai Chi and Bagua Thinking, which is the form of simulating Taiji Bagua. Many people think that the forms of these settlements derive from Tai Chi and

SPACE OBSERVATION-BASED GRAPHIC ANALYSIS OF THE SETTLEMENTS IN THE FORM OF BAGUA
By using satellite map observation technology like "Google maps" and "Baidu maps", we observed the forms of the settlements of Gaoyao region, and found that in this region, there exist many settlements of special forms that reminds people the Bagua. There are varieties of expressions of the Bagua diagram (Fig. 2), and the common distinguishing features of different Bagua diagrams are: • With clear morphological centers; • Showing radial cobweb form; • There is explicit relationship between the form and the location.   According to this definition, it is found that the actual number of such settlements in the form of Bagua in Gaoyao region is 35, which is more than the legendary number.
After collecting the statistics of the exact quantity and location of the settlements in the form of Bagua, the "Distribution of the Settlements in the Form of Bagua of Gaoyao " is plotted as below (Fig.  4).

ISOMORPHIC RELATIONSHIP
Found during the research, there are mysterious isomorphic relationships exist between the geographical en-vironment of Gaoyao and the distribution of the settlements in the form of Bagua.  5) could be obtained. It can be seen from the diagram that Gaoyao has a terrain that the northwest is higher than the southeast, the settlements in the form of Bagua are all located in the south of the Xi-jiang River with low altitudes, and there is no such type of settlements in region of higher altitudes.  Based on the two diagrams above, it is proven that important correlations exist between the land form and floods and the distribution of the settlements in the form of Bagua. We speculate that the formation of this form derives from the landform and flood prevention. 1 Light color indicates the region with lower altitudes; dark color indicates the region with higher altitudes. Red spots are the location of the settlements in the form of Bagua. 2 In June and July of 1915, an extreme flood occurred at Xijiang River; it is the worst flooding ever recorded for the River. Peak discharge of Wuzhou station reached 54500m3/s, which is the highest record in history; the dike of the Xijiang River almost all burst, with countless wound and casualities; the losses caused by the disaster was serious. As recorded by the "Amended County Annals of Gaoyao": "In the summer, exces-sive rain lasted for months, the Xijiang River rose suddenly and sharply, all the dikes of the county burst (include Jingfu dike and 35 other dikes). It was the most severe disaster since Daoguang Jiachen of Qing dynasty. The whole city was inundated, with water of several feet in depth in the city. Guangzhou was also impacted by the flooding because of the burst of Jingfu dike. 3 Drew by the author.

STUDY OF THE INHERERNT CAUSES OF THE FORMATION OF THE SETTLEMENTS IN THE FORM OF BAGUA
In the formation of traditional settlements, defense is the primary concern, and the objects of the defense in-clude natural and human disasters. Owing to the strong ancestral sense of the Cantonese, the forms of social or-ganization also played an important role in the formation of the forms of settlements.

4.1.
Defense of Floods Common natural disasters in Gaoyao include floods, droughts, storms, pests, etc. In the various natural disas-ters, floods are the most harmful, frequent and with the most far-reaching impact. Therefore, in the disaster pre-vention strategies of the settlements of Gaoyao, the most critical one is the defense of the floods.

Floods in Gaoyao.
Gaoyao is located in the middle and lower reaches of the Xijiang River. Xijiang River enters China from west-ern Gaoyao, meandering through the county, with up to 90km of length in the county. Xijiang River is a main stream of the Pearl River, which has the runoff that ranked the second in China, and the per capita water of the watershed ranks the first among the seven major rivers of China. Gaoyao region is located in the critical sector of the Xijiang River's main stream. The Xijiang River basin has the most frequent floods of the Lingnan area.
The climate of Gaoyao is mainly subtropical monsoon climate; subtropical monsoon brings abundant rainfall, making the average annual rainfall reach 1647.9mm; meanwhile the region suffers from the attack of typhoons every year, and the rainfall could reach more than 100mm in a short period of time. Flood season of the Xijiang River is April to September, contributing 83% of the annual rainfall; in particular, the rainfall of May, June, and August is the most, accounting for 48% of the annual rainfall.
The specific geographical environment and climatic conditions of Gaoyao caused constant serious floods for the region. Since the Song Dynasty, 33 times of large floods and 402 times of small floods are recorded, in aver-age one large flood for each 30 years, and one small flood for each 2~3 years. For the 202 years from the Qi-anlong 12th year (1747) to 1949, there were 56 years when the floods caused dike burst, the disaster incidence is 27.7%. The total farmland of Gaoyao is 748,700mu; along the Xijiang River and the two shores of Xinxing River, 637,200mu of farmland (85.1 of the total farmland) is threatened by floods.

Flood defense strategy of the settlements.
Gaoyao region is not only a typical mountainous and hilly zone in Guangdong region, with many hills of gentle slope in the territory, but also a typical water land in Lingnan area, with intensive rivers, lakes, and numerous low-lying wetlands. First, the villagers take advantage of towering mountains to form natural high pedestal, to protect the building from flooding; secondly, make use of mountain elevation difference to drain precipitation as quickly as possible, to prevent retained precipitation from affecting roads and building foundations; thirdly, make use of surrounding waterways and fish ponds to form protective ponds, to create stagnant water and water storage barriers of the Settlements.
The road system perpendicular to the contour line forms the shortest drainage channel with largest height dif-ference (Fig.7). The roads are paved with cobblestone or red sandstone, to achieve waterproofing and roadbed protection effect.

Defense of Human Disasters
For the defense of human disasters, the comb-like settlements of Guangdong is not superior, while Hakka Round House is the most typical defensive Settlements, but for the hot and humid climate in the Pearl River Delta, it has such disadvantages as poor ventilation and moisture resistance. The Settlements in the Form of Bagua, in fact, absorbs both advantages. It takes the form of island village surrounded by water, leaving only a few roads into the village, with towers and gates at the entrances (dismantled now), serving as the first level of defense; the doors of peripheral buildings are opened inward, with the peripheral buildings serving as the enclosing wall of the settlement. Several entrance gatehouses are set along the peripheral settlement, similar to Round House, forming the second level of defense; the internal roads in the settlement are full of twists and turns, and outsiders can easily be trapped, thus forming the third level of defense (Figure 8). The Japanese invaders were once trapped in Xiangang Village. From the morphological point of view, circular shape is the best for defense, with the spiritual function of in-ternal uniting. The form of Bagua is the best choice for settlements that fulfill optimal defense.

4.3.
Social Organizational Forms The Guangfu people have s strong clan tradition. The gathered dominant clan is divided into several branches. The clan has Ancestral Hall, and each branch has its Branch Ancestral Hall and Family Ancestral Halls (called "Ancestral Temple" by villagers). Xiangang Village has the most typical characteristics. There are 16 Ancestral Halls and the two Study Halls along the settlement periphery, known as "Bagua and 16 Ancestral Halls" (Figure 9), and scattered within the village are dozens of Ancestral Temples (more than 50 according to preliminary es-timation, requiring further investigation). Along the periphery of Licha Village, there are 10 Entrance Gate Tow-ers (called "nine Li and one Fang" 4 ) instead of large ancestral hall, and there are also 16 ancestral temples in the village ( Figure 10). The ancestral halls in Xiangang Village or gate towers in Licha Village, representing a clan, cut the whole settlements into several groups. These groups, just like their social relations, are not only divided and separated, but also fused and bound, jointly forming a dominant clan in the same region.

CONCLUSIONS
In summary, although the settlements in the form of Bagua in Gaoyao region have certain features of the Bagua of Tai Chi, they shouldn't be simply classified to settlements built with the idea of Tai Chi without tangible demonstration, where the essence of this form is ignored and the wisdom and experience of the ancestors who created these villages are cramped.
The most important inherent cause of the formation of the forms of settlements is disaster defending. The form of Bagua is actually a fortuitous product of the settlements' defense of floods. This study proposes the idea that the formation of the settlements in the form of Bagua has obvious inherent cause of natural and human disaster prevention, while adapting the forms of social organization; and during the development of the settlements, the influences of the Bagua of Tai Chi as well as Feng Shui are integrated, thus forming the current form of the Bagua. Creating optimal living environment is the nature of these settlements in the form of Bagua, and it is not in con-tradiction with the ideas of Fengshui. These settlements went through continuous enrichment and perfection and become such peculiar landscape. If the mysterious Fengshui of their appearance is constantly emphasized, the further exploration of the deeper meaning of these settlements might be impacted.