How do you determine what makes up a region

A region is an area of land that has common features. A region can be defined by natural or artificial features. Language, government, or religion can define a region, as can forests, wildlife, or climate. Regions, large or small, are the basic units of geography.

radiative zone

explanation    

radiative zone is the layer of the sun which energy is transferred away from the core by radiation. although, the core is the only part of the sun that produces an appreciable amount of heat through fusion. in fact, 99% of the energy produced by the sun takes place within 24% of the sun's radius.