Nowadays people often divide cities into first-tier and second-tier cities. The first and second lines are classified from the perspective of economics.
There are four first-tier cities in China, covering the north, Guangzhou and Shenzhen. Next is the second line. Chengdu, Hangzhou, Nanjing, Tianjin and Chongqing are all second-tier. Second-tier cities are not necessarily provincial capitals. Then the third line, Guiyang, Kunming, Nanning and so on.
Grades are divided according to administrative units. All provincial capital cities are first-class cities, and all other independent administrative regions are second-class cities. How to distinguish specifically? Telephone landlines have area codes, and car users have independent area codes. For example, Ziyang is Sichuan M, a secondary city.
What is a tertiary city? Dujiangyan is a tertiary city, Guanghan is a tertiary city, and Jiangyou is a tertiary city. They are named after municipal units, but their jurisdiction and scope still belong to other first-class or second-class cities.
Dujiangyan, Chengdu, the area code is 028. The photos are all from Sichuan A, Guanghan City, Sichuan, Deyang City, Sichuan F, and jiangyou city B, Mianyang City, Sichuan.
It is wrong to say that Baidu is a third-class city. Because now Ziyang just changed the area code of the telephone number to 028, but the license plate has not changed, and it is still Sichuan M. Now Ziyang is becoming a division of Chengdu, and it will become Ziyang District of Chengdu like Wenjiang and Qingbaijiang. So Ziyang is now a secondary city.