The platform imagineRio is a searchable atlas that illustrates the social and urban evolution of Rio de Janeiro over the entire history of the city, as it existed and as it was often imagined. Views of the city created by artists, maps by historical cartographers, and ground floor plans by architects –from iconographic, cartographic, and architectural archives– are located in both time and space while their associated visual and spatial data are integrated across a number of databases and servers including an open-access digital library of images, a geographic information system, an open source relational database, and a content delivery web service. The relationship between the various project elements produces a web environment where vector, spatial, and raster data are simultaneously streamed in, probed, toggled, viewed, or queried in a system that supports multiple and interconnected expressions of diverse data sources. It is an environment where, for example, historians can visualize specific sites of inquiry both temporally and spatially, where architects and urbanists can see proposed design projects in situ, where literary scholars can map out novels while visualizing their specific contexts, and where archaeologists can reconstruct their complex stratigraphy. Scaled down into a mobile app, tourists and residents will be able to walk about town while visualizing the city as it once was as well as it was once projected. Rio de Janeiro's urban history is particularly well suited to being captured in a diachronic web map environment considering how much the city's natural environment, urban fabric, and self-representation has changed over time. To make Rio what it is today, mountains were leveled, swamps drained, shorelines redrawn, ridgelines altered, and islands joined to the mainland, while the adjacent Tijuca Forest was first cleared for planting coffee and extracting charcoal only to later be replanted for the protection of the city's water sources. Such a changing physical and social landscape, with all its political consequences, lends itself to being spatially contextualized in a digital platform that maps and illustrates transformation over time.