*2.2. Data*

The data used in this paper include the population migration data, search query data, and socioeconomic data. (1) There are three kinds of population migration data used in this study: the net inflow population, intercity population flow, and the floating population. The net inflow population delineates the total population migrated into the city during a specific period. Intercity population flow is the population migrate from the original city to the terminal city. Based on the prevalent use of series Tencent's applications (e.g., Wechat is the most used software for 79.6% of Chinese netizens), more precise expression on the migration of population in China can be provided by Tencent migration map under the support of enormous user base. Considering the merit of Tencent migration map and avoiding the self-certification of Baidu, we obtained the net inflow population and intercity population flow from Tencent migration map (https://heat.qq.com/qianxi.php) through web crawler technology. Due to the specific Hukou policy in China (which has been regarded as the central mechanism underlying the unsettled nature of the floating population), the floating population has been defined as the population living in the objective city more than six months without local registered Hukou [35]. It was obtained through the deviance calculation of permanent residential population and household population in the local city, which were collected from regional statistical bureaus. (2) We obtain the search query data based on the support of Baidu search engine, which is the most widely used search engine in China and freely provides the search trend of objective terms through Baidu Index (http://index.baidu.com/). The average daily queries of each migration keyword versus the name of the city (e.g., job + Beijing) from 1 January 2015 to 31 December 2015 were collected based on Baidu Index. (3) Relevant socioeconomic data were acquired from regional statistical bureau, including the Tertiary Industrial Output-Value, Participant Rate of Urban Basic Medical Care System, the number of schools, etc. The migration reasons were collected from the dynamic monitoring survey of China's migration population in 2015, which was conducted by the National Health and Family Planning Commission of China.
