Our MRT map and that of many others around the world are based on Harry Beck’s London Underground map.
Below is Harry Beck’s Tube map in the sky.
It’s a Tube map of the sky published just a few years after his London Underground map. In aviation’s early days, planes stopped much more frequently, making stops “Such long-limbed networks naturally echo metro lines,” FT’s columnist in https://www.ft.com/content/ea87c244-1da0-11ea-81f0-0c253907d3e0 (Pay wall)