Line circle?

The Circle Line of the London Underground became known as such in 1949, when it was separated from its parent lines, the Metropolitan Line and the District Line, although it had been shown on Underground maps since 1947. It is often referred to as a "virtual line", as the Circle Line does not have any stations for its sole use. This is because the Circle Line was created from two previously-existing lines (see history below). The only two sections of track over which the Circle Line operates exclusively are the chords between High Street Kensington and Gloucester Road, and between Tower Hill and Aldgate. The line has interchanges with most of the major London terminals.