First founded in 1832 as a railroad line originally linking New York with its titular lake, Erie Railroad had undergone a period of explosive growth with the laying of more than 2,316 miles of track at its peak. Thanks to the invention of the telegraph in 1844, these tracks were overseen by a number of workers and superintendents, who were responsible for reporting information down the track about potential problems in order to prevent train wrecks and delays. But McCallum found it hard to keep track of who in his ever-expanding network of superintendents was responsible for what sections of track.
McCallum turned to design for an answer, and the result is what is (in the unwieldy style of the time) titled "The New York & Erie Railroad Diagram Representing A Plan Of Organization Exhibiting The Division Of Administrative Duties And Showing The Number And Class Of Employés Engaged In Each Department From The Returns Of September 1855." But don't let the stuffy title kill it for you, because this wonderful graphic--what historian Caitlin Rosenthal calls the "first modern organizational chart"--is a thing of beauty.
From a distance, McCallum's chart looks less like it deals with railroads than the blossoming of some exotic flora. A seed-like root of Erie Railroad's board of directors eventually sprouts into the office of general superintendent. From there, a number of sinuous vines grow, curling around the various trestles of the Erie Railroad's lines, which eventually fruit into groups of employees. It's beautiful information design that manages to look surprisingly modern.
For more information on McCallum and his organizational chart, read Rosenthal's article on big data in the age of the telegraph here. Sure beats your company's dusty CEO-topped pyramid chart, don't you think?