1.Increasing Demand For Urban Travel In a Decade

In the decade from 2009 to 2018, China added 69 civil aviation airports, and the total passenger throughput increased by 1.6 times.
In 2018, the number of cities with a throughput of over 10 million people has reached 37, and the passenger throughput of Beijing Capital Airport has finally exceeded 100 million. It has become the second airport in the world with a passenger throughput of over 100 million passengers after the Atlanta airport in the United States.

After examining all the changes in airport throughput and geographical location, we found that growth occurred around urban agglomerations or airport clusters. Although all airports have growth, Beijing-Tianjin-Hebei, Yangtze River Delta, Pearl River Delta and Chengdu-Chongqing, the advantages of urban agglomerations are becoming more and more significant.

2.2018 China Aviation Network Among Cities

Passenger throughput is more indicative of the activity of business travel activities, but if we want toit is not enough to measure the degree of hub of an airport. To assess the importance of an airport in this network, you also need to answer these questions: How far is a city connected through the airport? Who is more intimate with whom? What is the range of radiation power?

We use the concept of centrality in Network Analysis. Calculated from the relationship between the nodes，the centrality seeks to quantify the influence of every node in the network. We can take the airport as a node, and an aviation network is formed through the interweaving of airlines. We have comprehensively considered the number of airlines between airports in 2018, the number of inbound and outbound flights, and calculated the centrality of each airport. The greater the centrality, the greater the importance of the airport throughout the aviation network and the greater regional radiation capacity, which are the hubs of the entire aviation network.

Projecting the centrality of all airports onto the map, we found that the distribution of the airports’ centrality is characterized by high east and west low, south high and north low, which is similar to economic indicators.

4.TOP30 Centrality Ranking

According to the airport centrality, the top 2 ariports is respectively located in Beijing and Shanghai, Xi'an is ranked third, and the centrality is almost the same as Shanghai Pudong Airport. It is worth noting that the central rankings of Guangzhou and Shenzhen are not high enough. This means that although the activity of business travel is leading, the connectivity with other regions or the influence on other regions is not high enough.

Among the airports in 230 cities across the country, airports with a centrality ranking TOP 30 can be considered as hub-type airports. From the distribution of hub-type airport, we can see the more obvious characteristics of urban and regional influence

5.The Transportation Capacity And Degree Of Hubs Of Yangtze River Delta is Ahead of Beijing-Tianjin-Hebei

In 2017, the National Development and Reform Commission proposed that Beijing-Tianjin-Hebei, Yangtze River Delta and Pearl River Delta will form three world-class airport groups in 2025. By 2018, the development characteristics of these three airport groups are becoming more and more obvious.
In the aviation network, the Yangtze River Delta is undoubtedly the most influential urban agglomeration. The comprehensive strength of Beijing-Tianjin-Hebei is not as good as that of the Yangtze River Delta, and it is second in the regional competition.

As a community, the Yangtze River Delta has now built 16 civil airports, three of which are the highest level 4F airports. In 2018, the total throughput of the Yangtze River Delta airport group reached 229 million. Regardless of the overall number of airports, construction level or throughput scale, the Yangtze River Delta is ahead of the other two major airport groups.

From the point of view of the overall coordinated development of the airport group, the Pearl River Delta mainly relies on Guangzhou Baiyun Airport and Shenzhen Baoan Airport to drive the external relations of the whole Pearl River Delta region. Guangzhou Baiyun Airport, as the top airport in the region, accounts for 53% of the total throughput. Shanghai Pudong Airport has a lower throughput ratio of 32% in the Yangtze River Delta. This ensures the coordinated development of airports in the Yangtze River Delta, and the internal gap is not too large. The Beijing-Capital International Airport in Beijing, Tianjin and Hebei account for 70% of the total airport's throughput, and other airports do not contribute too much.

6.Another Core Airport Group is Located in Southwest

Chengdu Shuangliu Airport (No. 4) and Chongqing Jiangbei Airport (No. 5) ranked more than Guangzhou Baiyun. Kunming Changshui Airport (No. 7) and Guiyang Longdongbao Airport (No. 14) also ranked high. Chengdu Shuangliu International Airport started in 2011 with a continuous throughput of more than eight years in Shenzhen Bao 'an Airport, and has been on the top of the fourth place after more than the Shanghai Hongqiao Airport in 2015.
Behind the centrality and throughput, this land has begun to accelerate on the runway of economic rise, not only sitting on unique tourism resources, but also the commercial exchanges between Chengdu and Chongqing in recent years, the economic activity is dense, and it is becoming more and more attractive to talents.

7.Airports in Central China and Northeast China are Less Competitive

Compared with the fierce struggling among airports in East China, South China, and Southwest China, the Central and Northeast China seems “ fall into depression ”.
Central China’s Changsha Huanghua Airport (No. 12), Zhengzhou Xinzheng Airport (No. 13), and Wuhan Tianhe Airport (No. 22) are all hubs, but their strength is relatively average, lacking a more conspicuous regional leader. However, this is related to the dependence of geographical location on aviation and the diversion of developed high-speed rail, which does not absolutely explain the frustration of central China.
The geographical corner, the underdeveloped northeast of the high-speed rail, but there is no such reason, the hub airport in the center of the airport TOP30 in the middle and lower reaches, is actually another microcosm of the development in these years.

8.TOP10 Hub Cities

According to the flight routes between hub cities of the airport groups, we could observe the interactions among these cities on the aviation network. Major airport groups usually have strong connections. The flight routes between Chengdu-Chongqing and the cities in the three major airport groups (Beijing-Tianjin-Hebei, Yangzte River Delta and Pearl River Delta) indicated frequent business travels among hub cities. Further more, as mentioned before that more flights travel from Pearl River Delta to Shanghai, Chengdu-Chongqing is favored by Beijing-Tianjin-Hebei and Pearl River Delta travelers. If the radiation power of hub cities difines the level of each airport cluster, East China and Southwest China are undoubtedly the most powerful areas since the remote geographical locations request more long distant travelling. One the othe hand, although North China and Northeast China cities are close to Beijing, they are still facing the problem of weak connections on the aviation network.

9.Conclusion

The pattern of urban warfare has not changed much for many years, and the first-line is stable. Strong second-tier cities are eager to move, and the rankings are somewhat floating. This is the same in the aviation network.
However, it seems that there are still variables in the regional competition on behalf of the future. The radiation power of collective combat in the Yangtze River Delta is super strong, and the degree of integration will bring some expectations to the upgrading of urban agglomerations; The Pearl River Delta, where both males and females co-exist, is the second, has many possibilities after it joins the Dawan District of Guangdong, Hong Kong and Macao; The Chengdu-Chongqing twins are fascinating in the West, and there is potential for new industries, businesses and tourism development.
The regional development issues often discussed by Beijing-Tianjin-Hebei old-fashioned people are also reflected in the route network hub. Even if they have the strongest hub cities in the country, when talking about the overall energy level of the urban agglomeration, the combat effectiveness is often difficult to explode.
What is certain is that the competition in urban agglomerations is becoming more and more intense.