areal (adj.)

1530s, "vacant piece of ground," from Latin area "level ground, open space," used of building sites, playgrounds, threshing floors, etc.; which is of uncertain origin. Perhaps an irregular derivation from arere "to become dry" (see arid), on notion of "bare space cleared by burning." The generic sense of "any particular amount of surface (whether open or not) contained within any set of limits" is from 1560s. Area code in the North American telephone systems is attested from 1959.