Over the years, PeeringDB has become the canonical source of where networks providers list their presence, and willingness to interconnect/peer with others. It's an invaluable directory and we encourage networks to list themselves here, if they are involved in peering and interconnection. INX lists all the Internet exchange points, as well as their specific points of presence here, to help operators choose which sites are interesting to colocate at.
We use PeeringDB to bootstrap our provisioning process (ie. we populate our database with information that peers publish in PeeringDB.com). In particular, we capture the contact information, IRR Object, and max-prefixes that the peer has made available to the PeeringDB community. We do not insist that peers have a PeeringDB record, but do encourage this, and can assist peers in setting this up.
Furthermore, we publish nightly updates to PeeringDB that include a peer's IP addresses, port speed, and whether, or not, they are a BGP-RS peer. Peers that select the "Allow IXP update", as part of their PeeringDB account, will automatically have this information updated by us.