"a scientific device that allows us to make spatial generalizations based on artificial criteria that we establish for the purpose of constructing regions"
"The basic spatial unit in our world regionalization scheme. Each realm is defined in terms of a synthesis of its total human goegraphy -- a composite of its leading cultural,, economic, historical, political, and appropriate environmental features."
ALL regional boundaries are transitions zones. Some are large like the boundary between Sub-Saharan Africa and North Africa.