Thanks (!?!?) to the ongoing tube strikes some Londoners have resorted to walking to work! For this, they either use Google maps, or the #tubewalk diagram which did the rounds last week.
While the existing tube walk map is good, it only details the time between adjacent stations. Most journeys consist of many stations, often on more than one line. Consequently, you can not simply add the walk times together, as there are many shortcuts possible when making the journey on foot, which are not possible when taking the tube.
This grid shows the distance (as the crow flies) between all combinations of station, inside zone 1.
I hope it's useful to someone! (If you're a designer and want to help build a decent UI for this, then please let me know!)
Note: the more zones you wish to see, the longer the page takes to load. Please be patient!