Yes, which is the whole point of my question: how is this data compiled?
Just because it requires effort does not mean it can't be done in an open source way.
Just because it requires effort does not mean it can't be done in an open source way.
2) IP Spidering via traceroutes / RIPE/etc data.
3) Agreements with third parties that have IP/Address mapping due to data supplied from users. [least accurate]
That'd be my guess anyway.