As defined, strangely by the Chinese government: https://stats.tj.gov.cn/nianjian/2010nj/html/zbe03.htm#:~:text=Permanent%20Population,(over%20half%20a%20year).

Note: There doesn't have to be a permanent population there of >250 at market close for this market to resolve Yes, it suffices if there have been >250 people there for at least half a year.