It's geojson, Github renders that: https://github.blog/2013-06-13-there-s-a-map-for-that/ https://github.blog/2013-06-13-there-s-a-map-for-that/ Edit: I was wr

It's geojson, Github renders that: https://github.blog/2013-06-13-there-s-a-map-for-that/ https://github.blog/2013-06-13-there-s-a-map-for-that/ Edit: I was wrong, it's topojson as per the other reply, based on the data-type attribute that's set on the div outside the map