The Internet is constantly evolving and changing over time. Outages, attacks, upgrades, censorships, and policy changes modify the routing very frequently everywhere in the world. To give the possibility to the Internet Service Providers and to the network operators of monitoring such an evolving scenario, many organizations collect information on the routing changes and give free access to them. We propose, prototype, and evaluate a visual interface, called Upstream Visibility, to display such data. It is based on three views: (1) a Global View that, based on stacked area charts, gives the high level trend of the visibility of an IP prefix; (2) a Local View that allows the user to check the effects over time of the visibility of an IP prefix on specific locations of the network; and (3) a traditional graph Animation View. Also, we propose heuristics for producing such type of drawings, evaluating their effectiveness and performance against scenarios describing well-known Internet incidents. Further, we classify Internet issues and study how they are visualized with our interface. We then identify and describe visual patterns which can be used to spot networking issues at a glance.