The revised system provides in theory for an absolutely constant rate per ton mile. It is a rigid mileage tariff in every respect. The original MacGraham scale had been so in theory, but not in practice. As amended in conformity with a sound economic principle, it had, moreover, one important practical advantage over the original scale. It yielded more revenue at all the intermediate points.[409] Local rates would be higher as thus calculated than they were originally. It would be unjust to ascribe undue importance to this motive on the part of the roads in the adoption of the new system. That the plan yielded additional revenue, while obviously more just in theory, was naturally no objection to its acceptance. The fruits of all this process of adjustment are depicted upon the accompanying diagram. Viewing it in a large way, and reserving details for later consideration, we may compare it to a topographical contour map. The several rate zones are thus analogous to a series of levels or steps rising from east to west. Our cross section of these along a line from Pittsburg to Burlington, Iowa, makes this relation plain. Another cross section at right angles to the first from Louisville, Kentucky, to Lansing, Michigan, and beyond, shows how these levels are arranged in a plane from north to south. These steps form a sort of irregular amphitheatre opening toward the east, with its main axis lying in a direction slightly south of west toward St. Louis. Or, more correctly, these rate zones, pursuing our analogy to a topographical contour map, indicate a broad valley opening toward the east. Along the bottom of this freight-rate valley lie the great direct trunk lines converging from Chicago and St. Louis. Throughout the State of Illinois the valley opens up onto a plateau, somewhat grooved in the middle at Peoria, where the direct lines from the west cross a neutral field tributary neither to Chicago nor St. Louis exclusively. [Illustration: CROSS-SECTION THROUGH LOUISVILLE AND LANSING]