Table 3. The urban hierarchy and its evolution under web search activity.

Class	List of city in 2011	List of city in 2014	List of city in 2016
National centers	Beijing, Shanghai, Shenzhen	Shanghai, Beijing, Chengdu, Shenzhen, Xiamen	Shanghai, Shenzhen, Beijing, Chongqing, Xiamen, Chengdu
National sub-centers	Chengdu, Xi'an, Chongqing, Guangzhou, Hangzhou, Xiamen, Dalian, Harbin, Qingdao, Wuhan, Sanya	Chongqing, Xi'an, Hangzhou, Sanya, Wuhan, Qingdao, Dalian, Harbin, Kunming	Hangzhou, Xi'an, Sanya, Qingdao, Wuhan, Guangzhou, Harbin
Regional centers	Tianjin, Zhengzhou, Ningbo, Kunming, Lanzhou, Changsha, Nanchang, Hefei	Zhengzhou, Tianjin, Lanzhou, Ningbo, Changsha	Dalian, Tianjin, Ningbo, Nanchang, Changsha, Zhengzhou, Hefei, Nanning, Lanzhou
Regional sub-centers	Nanning, Changchun, Urumqi, Quanzhou, Xining, Fuzhou, Haikou, Hohhot, Yinchuan, Shantou,	Hefei, Nanning, Nanchang, Urumqi, Fuzhou, Xining, Quanzhou, Haikou, Yinchuan, Changchun, Hohhot, Shantou	Shenyang, Kunming, Quanzhou, Xining, Fuzhou, Urumqi, Haikou, Yinchuan, Hohhot, Changchun
Local centers	Lhasa,Shenyang,Yantai,Zhanjiang	Lhasa, Shenyang, Yantai, Zhanjiang	Zhanjiang, Shantou, Lhasa, Yantai