As sophisticated enterprise applications move to the Web, some advanced user experiences become difficult to migrate due to prohibitively high computation, memory, and bandwidth requirements. State-dependent visualizations of large-scale data sets are particularly difficult since a change in the client’s context necessitates a change in the displayed results. This paper describes a Web architecture where clients are served a session-specific image of the data, with this image divided into tiles dynamically generated by the server. This set of tiles is supplemented with a corpus of metadata describing the immediate vicinity of interest; additional metadata is delivered as needed in a progressive fashion in support and anticipation of the user’s actions. We discuss how the design of this architecture was motivated by the goal of delivering a highly responsive user experience. As an example of a complete application built upon this architecture, we present OrgMaps, an interactive sys...