Centre of Mileage and of Population.—The space for notes on the maps permits the bare mention of the meaning of the series of stars in the 1889 map ([page 433]), which mark the centres of mileage and of population. It is well to state the manner of determining the centres of mileage, that it may have its proper bearing in any study of the subject into which the showing may enter.
The locations are necessarily approximate. Each centre was determined by selecting, on the proper map, a line running east and west which seemed, to the eye, to nearly divide the mileage into equal parts. The sum of the mileage of the States north, was then compared with that of the States south of the line. By this means the position of the line chosen by the eye was corrected and the right parallel determined. The meridian dividing the total mileage into equal parts was ascertained in like manner. The point of intersection of the parallel and meridian is marked in the map by a star, having the proper date printed to the right of it.
The upper series of stars locates the centres of railway mileage, and the lower series the centres of population, as given by the returns of the census of 1880.
The following table describes the several locations thus ascertained:
Centres of Railway Mileage.
| Date. | Latitude. | Longitude. | Approximate location by towns. |
| 1840 | 40° 50′ N. | 76° 10′ W. | Twenty miles west of Mauch Chunk, Pa. |
| 1850 | 41° 30′ N. | 77° 27′ W. | Twenty-five miles northwest of Williamsport, Lycoming County, Pa. |
| 1860 | 40° 40′ N. | 82° 30′ W. | Ten miles south of Mansfield, O. |
| 1870 | 41° 10′ N. | 84° 35′ W. | Paulding, Paulding County, O. |
| 1880 | 41° 05′ N. | 86° 50′ W. | Thirty miles northwest of Logansport, Ind. |
| 1888 | 39° 50′ N. | 88° 40′ W. | Pontiac, Ill., about ninety miles S. S. W. of Chicago. |
The remarkable movement of the centre of mileage from 1850 to 1860 is easily understood when one turns to the maps of those dates ([page 430]) and locates the fields of activity. The wonderful increase in Ohio, Indiana, Illinois, Wisconsin, and Iowa gave the Western impulse, while the growth in Tennessee and the States south of it furnishes the principal explanation of the southerly motion.
Although the study of this period is the most interesting of the series, in the space passed over, yet each period has its points of special interest, which the reader will easily solve by referring to the proper maps on pages 430 to 433.
Railway Systems.—The consolidation of separate lines under central controlling interests has resulted in several "systems" of great extent. Five such are mapped on pages 434 and 435. The roads controlled by them are printed in broad lines, while all others are printed in narrow lines. It needs but a glance to see whether any of them has so far absorbed the roads of a given region as to be able to control rates. The systems selected are believed to be representative ones, and the mapping of a dozen others would not tell the story any more plainly.