The number next to the name of each station shows the ground level at that station relative to sea level. The coloured dots represent platforms on other tube lines at the same station, which really puts the difference between sub-surface and deep-level tube lines into perspective. The orange line on each diagram represents ground level, and the blue line is sea level which conveniently never changes , while the coloured line shows the position of the platform of each station below ground level, in metres. It's a well-known fact that Hampstead is the deepest station on the network — it can be seen above in all its glory 58m below ground level. The must-read London articles. The Bank branch of the Northern line above , for example, looks like a bit of a mess. Click for a larger version When you hopped on the tube on the way to work this morning, how deep below the ground did you go?