Rates which can be considered alone are comparatively few in number. In the large majority of cases they are interrelated with other rates, and frequently this interrelation exists as between areas widely separated. The rates upon iron and steel from mills within 50 to 100 miles of New York, Philadelphia and Baltimore, whose relations to each other are established by long custom and usage, are based primarily upon the necessity of preserving a fair comparative charge between the different shipping points and destinations. Rates upon coal from central Pennsylvania to tide water have close relations with the rates upon coal from West Virginia to tide water, competing as such coal does, in the same markets. The rates upon lumber from the Michigan markets must bear some relation to the rates on lumber from Louisiana and Georgia to the same market of distribution, although separated by hundreds of miles. The rates upon grain from western farms to eastern points bear a relation to the other, and upon export grain the rates to the Atlantic seaboard bear a close relation to the rates to the Gulf. The rates upon fruit and vegetable traffic from the various shipping districts, as California on the West and Florida on the South, must be considered in the making of rates. The structure of rates between the territory east of the Mississippi and north of the Ohio River, and the territory east of Pittsburg and Buffalo, including New England, is closely interrelated; as an example, the rates between Chicago and New York take a percentage of the Chicago rate from all points west of Pittsburg and Buffalo. The principle of the interrelation of rates has frequently been recognized in the decisions of the Interstate Commerce Commission. In the interest of the manufacturer there is a very important relationship between rates upon different products entering into the manufacture of a given article. In the great steel-producing districts of the Shenango and Mahoning valleys and Pittsburg for many years the rates upon raw material to the furnaces for the production of pig iron have been adjusted upon a basis, so far as possible, of making the freight cost of assembling the raw materials that enter into this product the same to each furnace. In the one case the rate upon coke may be higher and the rate upon ore or limestone lower; in other cases the reverse. The adjustment of rates upon these different raw materials is so made that when assembled at the different furnaces the aggregate cost is relatively the same. This illustrates the contention that such rates cannot be considered separately, but must be taken as a whole.