Ordnance Survey five-foot maps of London, with coloured manuscript additions showing underground railways. For the eastern end of the Central Line, sheets of the Ordnance Survey 1:2,500 County Series for Essex were used as the base maps.
As well as London Transport Underground lines, there are maps showing the Kingsway Subway (a tramway tunnel), the Post Office Railway, and the Waterloo and City Railway (then part of British Railways, Southern Region). A separate set of maps is used for each line. Details shown include the overall width of tunnels and the layouts of stations, including the positions of stairs, escalators and passageways for public use. Shafts and tunnels bored purely for construction reasons are not shown. The dates given in the catalogue entries are those when the annotations were made.