Imagine a map of the London Underground, No, not the map we normally see, that is just a graphic showing the differnent stations laid out in a simple order, bears no relation to where the tube goes in real life.
No a real map, in fact google maps, so you can drag and zoom, now what about adding where the tube trains are on those lines, in real time, where they are at this very moment?
Sounds a bit far fetched, well since Transport for London allows anyone to view their data about train arrivals and departures, and with a clever bit of mathematics, you can now see the tube trains moving around the underground system!
http://traintimes.org.uk/map/tube/