Last June, GitHub announced support for GeoJSON rendering just commit and you have a versioned, open-source map. Six months later, visual GeoJSON diffing followed suit. Since then, GitHub hosts hundreds of thousands of GeoJSON files, has served millions of maps, and has diffed tens of thousands of changes, both proposed and realized. Why GeoJSON? Why Leaflet? Why openstreetmap? We'll take a look at both the technical how, and the philisophical why, and pull back the curtain on GitHub's recent venture into the world of GIS.