Though I have seen many articles, web pages, and other tables that detail which networks are 'peering,' I have never seen an accurate representation of this type of data from a third party.
amen!
To further complicate matters, many networks out there are mis-representing themselves as [cost-free-] peering with other networks when they are actually customers, or in some type of 'settlement' arrangement.
i contend that one can count the true tier one networks on the fingers of two hands.
As for your second question about the locations that networks interconnect, many networks consider this information sensitive as well-- though during your conversations with them, they will typically exchange that data with you-- though probably under a mutual NDA. Some choose to peer in locations where it is the most cost-effective between the two networks, while others peer in a smaller set of locations that make sense from a network hierarchy/topology perspective. The decision about whether to peer with a given network privately/directly versus at a public exchange point is often based on the amount of traffic to be exchanged, the network coverage area, and other such criteria.
With a bit of knowledge, tools, routing table vantage points, and time, you should be able to find out most of what you want to know on your own.
You might start by asking the operators of the exchange points (where you intend to connect) who their current customers are-- then you can contact those networks individually. Some exchange points will give you an "I want to peer with you" form and a list of e-mail addresses, so that you can mass-request.
Don't get cook'ed by the wealth of misinformation out there.
people should spend the tree and print jsb's message and frame it. randy