In 1949, the service was separately identified on the tube map as the Circle line for the first time.
Young men with switchblades and tube maps had existed in all ages.
Today's tube map is an evolution of that original design, and the ideas are used by many metro systems around the world.
The line began appearing on most tube maps, from the mid-1930s.
A good example is the tube map of the London Underground.
Circle line appears on tube maps as a separate service for the first time.
The river was reinstated on the tube map in 2009 after a public outcry.
However, separate names are used on station entrances, platforms and the tube map.
The iconic tube map designed in 1931, was published in 1933.
The suffix was dropped from tube maps in the 1960s.