Unusual and highly detailed map of the two cities, showing streets, Rail lines, stations, bridges, dams, locks and other details. Apparently produced by or drawn from a map in the City Engineers Dept in Pittsburgh. A wonderful, highly detailed city map.
O. W. Gray was a publishing firm based in Philadelphia. Later, they published as O. W. Gray & Son. They published atlases in the late nineteenth century. Gray's National Atlas was one of the most successful commercial ventures of the 1870s and one of the last to employ hand coloring on maps.