Explain Why Did The London Tube Map

Why did the london tube map become 'an iconic image of london'?
The Tube Map, formally known as the London underground map, is the map which represents the lines and stations of the London Underground - London's rapid rail transit system. It is a simplified map which is not strictly accurate in terms of geography, but effectively shows the relative position of stations through the graphical approach using representation of artificially straitened route lines which are placed vertical, horizontal and diagonally, each line is represented by a color.

The London tube map become the first diagrammatic representation of an entire rail transport network in the world, the design is treated as the 'London classic design'.
It became an iconic image