The DNS Core Census is an ICANN project to gather information about top-level-domains (TLDs). This covers ccTLDs, gTLDs, effective TLDs (like co.uk), and entries in arpa. The census contains information about the zone, like metadata and contractual information, about the name servers, about addresses of the name servers, and the route origins. The data is kept for a 35-day rolling window.

Further information about the project can be found in this presentation and OCTO-019 from ICANN's Chief Technology Officer