Last Thursday, Ben Balter wrote:
Not long ago, we began rendering 3D models on GitHub. Today we're excited to announce the latest addition to the visualization family - geographic data. Any .geojson file in a GitHub repository will now be automatically rendered as an interactive, browsable map, annotated with your geodata.
Wow! GitHub, MapBox, OpenStreetMap, Leaflet, and GeoJSON are five of my favorite things on the web. I can't wait to see what happens next.
Update (2013-06-25): GeoJSON previews for CKAN datasets
Update (2013-06-26): Marker clustering and TopoJSON support are what's new at GitHub