GeoJSON encodes geographic features (points, lines, polygons) as JSON objects following RFC 7946 (2016). Coordinates are always [longitude, latitude] in WGS84. Supported natively by Leaflet, Mapbox GL, OpenLayers, ArcGIS, QGIS, and PostGIS — the default exchange format for web mapping. Lighter and easier to inspect than KML or shapefile (.shp).
How to open
GitHub renders GeoJSON files inline as interactive maps. geojson.io provides an in-browser editor + validator. QGIS opens .geojson directly. Leaflet/Mapbox apps consume it programmatically.