I like this bird’s eye illustration showing potential additions and extensions to the existing IRT and BMT subway lines. For a good look at how the subways lines grew and changed over time, check out nycsubway.org‘s archive of historic subway maps.
ALL ROADS LEAD TO TIMES SQUARE: The Pending Subway Offers Make It a Focal Point for the Transit Development of the Future — A Bird’s-eye View Showing How Proposed Lines, if Carried Out, Would Lead to Times Square. (PDF)
From April 2, 1911