This is a map of the Cleveland, Cincinnati, Chicago and St. Louis Railway (Big Four) drawn on the New York Central system as of 1918, with trackage rights in purple. Email me if you would like a copy of the GIS data I created (modified from Bureau of Transportation Statistics North American Transportation Atlas Data) or if you see any errors.
This map includes all companies leased by the Big Four, as well as the following operating subsidiaries:

Central Indiana Railway (jointly controlled with the Pennsylvania Company)
Cincinnati Northern Railroad
Kankakee and Seneca Railroad (jointly controlled with the Chicago, Rock Island and Pacific Railway)It does not include the following:

Dayton and Union Railroad (the Baltimore and Ohio Railroad took majority control in about 1918)
No machine-readable source provided. Own work assumed (based on copyright claims).
No machine-readable author provided. NE2 assumed (based on copyright claims).