on what basis is a particular country divided into different geographical and administrative regions​

Administrative division,[1] administrative unit,[2][3][4] country subdivision,[5] administrative region[citation needed], subnational entity[citation needed], first-level subdivision[citation needed], as well as many similar terms, are generic names for geographical areas into which a particular, independent sovereign state (country) is divided. Such a unit usually has an administrative authority with the power to take administrative or policy decisions for its area