My point was that competing, differently-named and organisationally-separate suppliers of network services frequently use common suppliers for metro fibre, long-haul transport, building access, etc. Just because you buy different services from different providers doesn't mean there will be no common points of failure.
Fate sharing is bad. The only way to be sure you aren't fate sharing is to request GIS data from the carriers. And even that could be wrong...
Tell your carrier that you want to buy physical seperacy. Currently this is only offered by some metro networks because corporates want physical seperacy to connect their SANs (Storage Area Networks) to their offices. My company's network maintains seperacy for the financial market data feeds that run across it. We do that because the customers specifically demand that capability. Rather than trying to do the carrier's job by requesting GIS data, tell them you want to buy "physical seperacy" as a product. Get them to do the work and show you the data to prove that they really are delivering physical seperacy. --Michael Dillon