zone [Gr., = girdle], in geography, area with a certain physical and/or cultural unity that distinguishes it from other areas. The division of the earth into five climatic zones probably originated (5th cent. B.C.) with Parmenides, who recognized a torrid zone (see tropics) and north and south temperate zones and postulated north and south frigid (or arctic) zones; his classification was adopted by Aristotle and is still in use. The zones are based on latitude: the torrid zone lies between 231/2°N and 231/2°S, the temperate zones between these parallels and the polar circles (661/2° N and S), and the frigid zones from the polar circles to the poles. Later geographers, recognizing that climate is affected by such conditions as altitude, distance from water, prevailing winds, and ocean currents, have used other bases for zoning. Most geographers today recognize five major climatic groups, based mainly on the work of the German meteorologist Wladimir Köppen. Two of these groups—the rainy tropics and the dry tropics, which encompass four different climates—together correspond roughly to the former torrid zone. Two humid climate groups of the Köppen system, encompassing six climates, together correspond roughly to the former temperate zones. Köppen's two polar climates correspond roughly to the two former frigid zones. In addition to the five groups encompassing twelve climates, geographers also recognize a series of highland zones where many of the other climates of the world are duplicated. Geographic zones in which people have similar patterns of life are called culture zones or areas (see culture). An example would be the plains area of North America.