Systems and methods are described to enable routing of network communications in a content delivery system in a manner expected not to exceed the capacity of individual communication links of points of presence (POPs) within the content delivery system. Specifically, a route mapping service is disclosed that can determine the effect of potential DNS records on volumes of traffic expected to reach a POP through individual communication links, and that can alter DNS records such that the expected traffic does not exceed a capacity of those individual communication links. Illustratively, the DNS records may be altered at a level of individual DNS resolvers interacting with the content delivery system, and the volumes of traffic expected to reach a POP through individual communication links can be determined based on a volume of traffic of client computing devices associated with an individual DNS resolver.