Leave it to Wired Magazine to distill the information for us:
"The panoramic photo of London comprises of 48,640 individual frames, which were taken on four Canon EOS 7D cameras over three days shortly after the London 2012 Games, and stitched together over several weeks. For any keen shutterbugs, the cameras were fitted with EF 400mm f/2.8L IS II USM lenses and Extender EF 2x III teleconverters, and mounted on Rodeon VR Head ST robotic panorama heads."
To make it a bit more accessible, your iPhone 5 takes 8 mega-pixel photos. This photo is 320 gigapixels. If it was printed, it would measure 98 by 24 metres. And it would be a waste to show you the photo here, since none of the panorama, and, shall we say, fascinating features, would be seen.
So click here to see the photo in its full scope. (And just click on that pesky box to close it.)