This visualization of Indian Railway Network was created by Arun
Ganesh. Arun has even includind instructions on how the image was
created. http://commons.wikimedia.org/wiki/File_talk:Indian_Railway_Network_Coverage_on_OSM.png
This is a Featured image, which means that it has been identified as
one of the best examples of OpenStreetMap mapping, or that it provides
a useful illustration of the OpenStreetMap project.
If you know another image of similar quality, you can nominate it on
Featured image proposals.
http://wiki.openstreetmap.org/wiki/Featured_image_proposals
Photo is CC-by-sa Arun Ganesh, National Institute of Design Bangalore
Done a splendid job