Generally, aspects of the invention involve creating a data structure (a map) that reflects routing of Internet traffic to Anycast prefixes. Assume, for example, that each Anycast prefix is associated with two or more deployments (Points of Presence or PoPs) that can provide a service such as DNS, content delivery (e.g., via proxy servers, as in a CDN), distributed network storage, compute, or otherwise. The map is built in such a way as to identify portions of the Internet (e.g., in IP address space) that are consistently routed with one another, i.e., always to the same PoP as one another, regardless of how the Anycast prefixes are deployed. Aspects of the invention also involve the use of this map, once created. The map can be applied in a variety of ways to assist and/or improve the operation of Anycast deployments and thus represents an improvement to computer networking technology.