I saw a show about him on TVO about a year ago. They brought him into a helicopter and flew over London for about 15 minutes, and over the course of a week he drew a 10 foot wide panorama of the City, from memory, with details right down to individual rowhouses. You can watch the video of it
here. (London Panorama, top right.) Aside from his amazing drawing, there are lots of cool aerial shots of the city.