Japanese cities

A city (市, shi) is a local administrative unit in Japan. Cities are ranked on the same level as towns (町, machi) and villages (村, mura), with the difference that they are not a component of districts (郡, gun). Like other contemporary administrative units, they are defined by the Local Autonomy Law of 1947.

Article 8 of the Local Autonomy Law sets the following conditions for a municipality to be designated as a city:

The designation is approved by the prefectural governor and the Minister for Internal Affairs.

A city can theoretically be demoted to a town or village when it fails to meet any of these conditions, but such a demotion has not happened to date. The least populous city, Utashinai, Hokkaido, has a population of six thousand, while a town in the same prefecture, Otofuke, Hokkaido, has nearly forty thousand.

Under the Act on Special Provisions concerning Merger of Municipalities (市町村の合併の特例等に関する法律, Act No. 59 of 2004), the standard of 50,000 inhabitants for the city status has been eased to 30,000 if such population is gained as a result of a merger of towns and/or villages, in order to facilitate such mergers to reduce administrative costs. Many municipalities gained city status under this eased standard. On the other hand, the municipalities recently gained the city status purely as a result of increase of population without expansion of area are limited to those listed in List of former towns or villages gained city status alone in Japan.

...
Wikipedia