Note: This was first published in 2018, so doesn't include additions to the network since then.
When you hopped on the tube on the way to work this morning, how deep below the ground did you go? 10m? 20m? More?
It depends which tube line you're on — and which part of that line. Now one Londoner has plotted the depth of every station on the network, and put the information into TfL-lookalike diagrams of each line, or section of the line.
Daniel Silva used data from TfL's own spreadsheets to put the diagrams together, simplifying it to make it more useful for the average tube passenger, rather than the engineers who usually make use of the data.
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. The number next to the name of each station shows the ground level at that station relative to sea level. So in the example above, the ground level entrance to Earl's Court station is 8m above sea level, and the station platform is 6m below ground 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.
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. Where these diagrams prove useful is showing how the geography of London affects the depth of the tube — the entrance to Hampstead station, for example is at the top of a hill, hence the large distance between the station entrance and the tracks below.
We could spend all day looking at the diagrams and puzzling over the quirks they throw up. The Bank branch of the Northern line (above), for example, looks like a bit of a mess. This is due to the platforms for different directions on the same line sitting at slightly different heights.
If you don't spend enough time on the tube, you can buy Daniel's diagrams as prints and posters too.