A bounded area within a larger ground — territory with edges, named so that things can be placed and found.
Latin regio (a direction, a boundary, a district), from regere (to rule, to direct, to keep straight); a region was first a line ruled out, and the bounded ground it enclosed followed from the line.
A bounded area within a larger ground, given edges so things placed inside it can be found. The root's ruled line is still the whole idea: a region exists because a boundary was drawn somewhere.