If you live in a city, you've probably experienced stepping onto a crowded train platform and feeling like a fish in a school, with everyone trying to swim the same direction. That's a pretty accurate image, according to this new visualization of commuters on the London Tube.

The video below, created by coder Will Gallia, depicts a single day's worth of traffic on the London Underground in 2009—562,145 journeys in all. Gallia used data from a 5% sample of Oyster-card journeys to estimate where most travelers' trips started and ended. Each tiny, colorful pixel represents a single commuter, although they might as well be blood vessels in a network of arteries, or ants tunneling through the ground.

As Gallia explains on his website, this project had many phases, and took nearly three years to complete. First, he wrote a routing algorithm in Python that searched for the shortest trips between two locations, mapping each journey as a set of points. He then wrote a shading program to compute and render all of the routes, used Photoshop to scrub away the lines of the original Underground map, and added some background music.

The result is a living, breathing transit map where commuter's bodies illuminate the shape of the Tube during the daily ebbs and flows of traffic. Personally, my favorite bit is midnight, when the last late commuters peter out and the Tube runs dry. [Will Gallia via City Lab]