The 12 world geographic realms are: Europe, Russia, North America, Middle America, South America, Sub-Saharan Africa, North Africa/Southwest Asia, South Asia, East Asia, Southeast Asia, Austral Realm, and Pacific Realm.  Geographers divide the world into geographic realms based upon contiguity of landmass and human and physical characteristics of the earth within each section, or realm.  As the classification system is based upon the surface of the earth, it reflects spatial relationships, and allows for construction of a framework based upon both human and physical characteristics. 

The division of the world into 12 distinct realms helps to provide a broad outline for understanding the way the planet formed and the manner in which humans have occupied it over thousands of years.  Within each realm, there are identifiable characteristics among people, reflected in the establishment of political boundaries separating them.