3.1 Relationship between city distribution and environment
Settlement site selection is demonstrated to be affected by many factors, including altitude, slope or aspect, water source, and soil [20]. As the most important form of settlement sites, city site selection is also restricted by these geographical factors. Based on the analysis of 64 cities in the Central Plains region, the relationship between cities and these geographical factors is obtained, which provides an important basis for analyzing city site evolution.
(1) Altitude
Human beings can only survive in conditions with appropriate temperature and pressure. Since the pressure and temperature gradually decline with the rise of altitude, human beings have to live in certain areas with an upper limit of altitude. The tool of extracting multiple values to points in ArcGIS 10.5 is used to extract the altitude data of each city site (Table 1).
Table 1. Altitudes of cities in the Central Plains region
Altitudes (m)
|
Yangshao Period
|
Longshan Period
|
Xia and Shang Dynasties
|
0-100
|
2
|
8
|
6
|
100-200
|
11
|
11
|
14
|
200-300
|
1
|
2
|
1
|
300-400
|
2
|
0
|
0
|
400-500
|
1
|
0
|
1
|
As shown in Table 1, the altitudes of cities in the three periods are all below 500 m, which is quite different from the altitude of the settlement distribution in this area published in previous studies [7]. Most of the settlement sites are below 500 m, but there are also a large number of settlements above 500 m. This is related to the flat terrain that is often required for the construction of the city site. Moreover, the altitude range of 100-200 m is seen with the largest number of city sites, which might indicate this range to be the most suitable for human habitation. In the Yangshao period, the average altitude of the city site is 199 m, the lowest is 51 m in the Dahecun site in Zhengzhou [21], and the highest is 478 m in the Zhouli site in Luoyang [122]. There are only two cities below 100 m and three cities above 300 m. In the Longshan period, the average altitude of the city site is 123 m, the lowest is 47 m, which is the Pingliangtai site in Huaiyang [23], and the highest is 260 m, which is the Wangchenggang site in Dengfeng [24]. Compared with cities during the Yangshao period, those in the Longshan period have much lower altitudes, and there are eight city sites below 100 m whereas there are no city sites above 300 m. During the Xia and Shang Dynasties, the average altitude of the city site is 136 m, the lowest is 74 m, which is the Huanbei Shangcheng site [25], and the highest is 467 m, which is the Nanwa site in Dengfeng [26]. Compared with cities in the Longshan period, those in the Xia and Shang Dynasties have slightly higher altitudes.
(2) Water
The settlement should not be too far away from the river for the convenience of taking water, while it should also not be too close to the river for the sake of flood control [27]. The horizontal distance from each city site to the river in three cultural periods is obtained in the DEM data of a 30 m resolution using the proximity near tool in ArcGIS 10.5 (Table 2).
Table 2. Horizontal distances between city sites and rivers in the Central Plains region
Periods
|
Yangshao Period
|
Longshan Period
|
Xia and Shang Dynasties
|
Horizontal distance from rivers (m)
|
Number
|
Percent
|
Number
|
Percent
|
Number
|
Percent
|
0-500
|
1
|
5.56%
|
5
|
23.81%
|
6
|
27.27%
|
500-1000
|
5
|
27.78%
|
4
|
19.05%
|
1
|
4.55%
|
1000-2000
|
5
|
27.78%
|
4
|
19.05%
|
3
|
13.64%
|
2000-3000
|
2
|
11.11%
|
4
|
19.05%
|
2
|
9.09%
|
3000-5000
|
3
|
16.67%
|
2
|
9.52%
|
5
|
22.73%
|
>5000
|
2
|
11.11%
|
2
|
9.52%
|
5
|
22.73%
|
Most of the cities are distributed within a distance of 3 km from rivers, accounting for 72.2% in the Yangshao period, 81% in the Longshan period, and 54.6% in Xia and Shang dynasties (Table 2). In the Yangshao period, this distance ranges between 257 m and 6780 m, with an average of 2253 m. During the Longshan period, this distance ranges between 192 m and 6459 m, with an average of 1946 m. During the Xia and Shang Dynasties, this distance ranges between 114 m and 9245 m, with an average of 3189 m.
3.2 Evolution of types and shapes of moats
3.2.1 Evolution of moat types
There were 18 cities in the Yangshao period, and among them, two cities were moated with walls, which were the Xishan City site [28] and the Longshangang site in Xichuan [29], respectively. The Xishan City site is the earliest walled settlement found in the Central Plains region, which is located 23 km away from the northern suburb of Zhengzhou City [30]. In the construction of city walls, ramming, plate building, and trenching were adopted [31]. In the Longshan period, the city wall began to appear in large numbers. There were 13 trench sites, including the Wangchenggang site[24] and the Guchengzhai site[32]. In the Xia and Shang Dynasties, there were 11 cities moated with trenches and 8 cities with city walls. There were also 3 cities without trenches and city walls, which were the Erlitou site in Yanshi [33], the Yinxu site in Anyang [34], and the Xiaoshuangqiao ruins [35].
Table 3. Types of moats in cities from ancient states to the kingdom in the Central Plains region
Periods
|
Trench
|
City wall
|
No trench nor city wall
|
Yangshao period
|
16
|
2
|
0
|
Longshan period
|
11
|
13
|
0
|
Xia and Shang Dynasties
|
11
|
8
|
3
|
3.2.2 Evolution of moat shapes
Moat shapes are reconstructed either according to the excavation report of the city, such as the Wangchenggang site in Dengfeng[24], or the remote sensing data, such as the Guchengzhai site[32].
Table 4. Shapes of moats in cities from ancient states to the kingdom
Periods
|
Rectangle, square, or trapezoidal shape
|
Irregular shape
|
Ringlike or circular shape
|
Uncertain shape
|
Yangshao Period
|
0
|
0
|
7
|
11
|
Longshan Period
|
13
|
0
|
2
|
9
|
Xia and Shang Dynasties
|
10
|
2
|
3
|
7
|
During the Yangshao period, there were 18 cities in total, of which 7 were circular in shape (Table 4). During the Longshan period, there were 24 cities, of which 13 were rectangular, square, or trapezoidal, while 2 were circular. In the Xia and Shang Dynasties, there were 22 cities, of which 10 were rectangular, square, or trapezoidal, 3 were circular, and 2 were of irregular shapes. Therefore, it could be indicated that there was a tendency of transitioning circular cities to square cities in the Central Plains region.
3.2 Evolution of city sizes
Table 5. Sizes of cities from ancient states to the kingdom in the Central Plains region
Size
|
Yangshao Period
|
Longshan Period
|
Xia and Shang Dynasties
|
0-25 hecares
|
12
|
14
|
9
|
25-50 hecares
|
5
|
5
|
5
|
50-100 hecares
|
0
|
3
|
3
|
100-200 hecares
|
1
|
2
|
3
|
>200 hecares
|
0
|
0
|
2
|
During the Yangshao period, all the 18 cities were relatively small, with slight differences in sizes among different cities and an average area of 20 hectares. There was only one city that was larger than 50 hectares, namely the Shuanghuaishu site. The cities with larger sizes were mainly distributed in the Yellow River and Yiluo River areas, while the cities in other areas were relatively small.
During the Longshan period, the average city size reached 39 hectares. There were 5 cities with areas of more than 50 hectares, including the Shaochai site (200 hectares) in Yiluo River Basin [36], the Wadian site (130 hectares) in Yinghe River Basin [37], the Xinzhai site (100 hectares) in Shuanghe River Basin [38], the Mengzhuang site (100 hectares) in Northern Henan [39], and the Pinggaotai site (91 hectares) in Southwest Henan [40]. There were obvious differences in the sizes among the cities, which can be classified into four grades. Moreover, there are generally fewer larger cities and more smaller cities.
During the Xia and Shang Dynasties, the average city size increased significantly to 340 hectares. There were three cities with areas of more than 200 hectares, namely the Anyang Yin Ruins in the north of the Henan Province with an area of 3600 hectares, the Zhengzhou Shangcheng ruins [41] in the east of Songshan Mountain with an area of 2500 hectares, and the Erlitou site [33] of Yanshi in Luoyang, with an area of 350 hectares.
3.3 Characteristics of city agglomeration
It can be seen from Table 6 that the NNI statistics of the cities during the Yangshao period and Xia-Shang dynasties are all less than 1, the Z score values are all less than 0, and the results all pass the test of the significance level of 0.01. Therefore, cities during these two periods are in a state of agglomeration. In the same study area, a larger NNI value corresponds to a lower degree of agglomeration of sample points. The agglomeration of cities during the Yangshao period is more obvious than that in Xia and Shang Dynasties. The NNI value of the cities in the Longshan period is greater than 1, and the Z score value is greater than 0. Therefore, cities in this period are distributed in a decentralized way. Thus, the degree of agglomeration of cities from high to low is: Yangshao period > Xia and Shang dynasties > Longshan period.
Table 6. Average nearest neighbor distances of cities from ancient states to the kingdom in the Central Plains region
Periods
|
Number of samples
|
Average nearest neighbor distance (m)
|
Expected average nearest distance (m)
|
NNI statistics
|
Z value
|
Yangshao Period
|
18
|
24640
|
34608
|
0.712
|
-2.338
|
Longshan Period
|
24
|
43477
|
35229
|
1.234
|
2.19
|
Xia and Shang Dynasties
|
22
|
22711
|
25664
|
0.885
|
-1.03
|
3.4 Evolution of gravity centers of cities
As is shown in Figure 6 and Table 7, the center of gravity of the city moved from the northwest during the Yangshao period to the southeast during the Longshan period, and further moved to the north during the Xia and Shang dynasties, reaching the proximity of the Songshan Mountain. This further confirms that the core cultural area of the Henan Province should lie in the area around the Songshan Mountain, which occupies a core position in the cultural development from the Neolithic to Xia and Shang Dynasties.
Table 7. Centers of gravity of cities from ancient states to the kingdom in the Central Plains region
Period
|
Displacement of the city center of gravity (km)
|
City moving direction
|
Yangshao to Longshan Period
|
67
|
Northwest-southeast
|
Longshan Period to Xia and Shang Dynasties
|
49
|
Southwest-northeast, near due north
|