I created a GeoJSON extraction interface for Smallworld. Its core is the method
.as_geojson(_optional out_stream) on the main geometry type mixins.
The GeoJSON Specification is available on geojson.org. It is a 10-minute read and it is easy to implement.
My product is on my github page. Loading the
geojson module adds functionality to the relevant exemplars. Example usage is.
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This prints all roads with fields of the default visibility tag as a feature collection. geojson.io is a cool page to verify and view your GeoJSON data. It can also give a good impression of the load on a browser, when many Geometries are rendered.