GeoJSON is a format for describing geo-data using JSON.
In 2015, the IETF (Internet Engineering Task Force) and a group of authors of the original specification joined together to form the GeoJSON Standardization Working Group. In 2016 they published RFC7946 “The GeoJSON Format”: https://tools.ietf.org/html/rfc7946
This is where you can interactively create/debug GeoJSON: https://geojson.io
By the way, as of 2019, this is the format Apple recommends adding data to the map when using their MapKit/MapKit JS: https://developer.apple.com/videos/play/wwdc2019/236/
Moreover, Apple has created a GeoJSON-compatible IMDF (Indoor Mapping Data Format) for describing rooms: https://register.apple.com/resources/imdf/
Go library: https://github.com/paulmach/go.geojson