Barcelona design firm 300.000 Km/s created the Historic Charter of Barcelona to explore the city’s history through cartography. Cross-checked for accuracy by the Barcelona City History Museum, the site presents a selection of 26 representative maps from texts, historical cartography, archaeological maps and contemporary digital maps. A timeline provides the main navigation, enabling visitors to watch the map expand as they move towards the present day. Built in open source geographic information system software such as OpenLayers, TileStache, Mapnik and SpatiaLite, the Historic Charter can superimpose maps from different eras as well, providing a great resource for communication, pedagogical support and research purposes.