GeoJSON is a widely-used format for encoding geographic data. It's flexible and human-readable, and because it's just JSON it's easy to integrate into web applications.
But it has some real warts, and if we wanted to we could certainly come up with a better format. After tweeting about my frustrations, I was asked to elaborate. Here goes:
GeoJSON geometries can be one of seven types: Point, MultiPoint, LineString, MultiLineString, Polygon, MultiPolygon and GeometryCollection.