Will Gallia has created this fascinating animation of over 500,000 tube journeys from TfL Oyster data. Each point represents a person and their movement over the course of a day, viewed on the map we're all so familiar with.
Will's website explains how he did it — a 5% sample of journeys in 2009 with a routing algorithm applied — and a lot of hard work.
https://vimeo.com/121462010