This is the legacy version of twitter.com. We will be shutting it down on 15 December 2020. Please switch to a supported browser or device. You can see a list of supported browsers in our Help Center.
Oli Hawkins Sep 30
Thanks Ali. It’s Leaflet and vanilla JavaScript transpiled and polyfilled to work in older browsers. The tiles for the base layer are served from Mapbox. In this case the boundaries are just simple geojson (i.e. not a tile layer). Carl created the boundary layer in QGIS.