English: Map showing the New York City Subway's "H System" that was implemented on August 1, 1918 (as part of the network if the Interborough Rapid transit Company).
The map shows lines from the IRT Broadway-Seventh Avenue Line (in red) and of the IRT Lexington Avenue Line (in green). The IRT 42nd Street Shuttle is in grey, and corresponds to the horizontal bar of the "H". End stations are also mentioned.
Originally, only dark red and dark green sections were completed between 1904 and 1908. Light red and light green sections were subsequently added and were put into service on August 1, 1918, thus joining the two halves of the Broadway – Seventh Avenue Line.