They have a link to a study of the major internet routes in the US and the name of the PDF is 'tubes_final.pdf'
That made me laugh.
"Long-haul fiber-optic cabling. Red squares mark where cables connect in nodes, many in major population centers. University of Wisconsin and ACM SIGCOMM, 2015. http://pages.cs.wisc.edu/~pb/tubes_final.pdf "