OpenStreetMap has contributors all over the world, and our biggest UK contributor is London-based courier firm eCourier. They kindly provide us with GPS data collected by their couriers, and when you edit a part of London it’s almost certainly thanks to them that the roads are so clear and easy to trace.
We made a short animation to illustrate a sample of their data which they are hosting here, and you can check out their site and read more about our collaboration on their news page.