Description

Returns a geometry as a GeoJSON "geometry" object, or a row as a GeoJSON "feature" object.

The resulting GeoJSON geometry and feature representations conform with the GeoJSON specifications RFC 7946, except when the parsed geometries are referenced with a CRS other than WGS84 longitude and latitude (EPSG:4326, urn:ogc:def:crs:OGC::CRS84); the GeoJSON geometry object will then have a short CRS SRID identifier attached by default. 2D and 3D Geometries are both supported. GeoJSON only supports SFS 1.1 geometry types (no curve support for example).

The geom_column parameter is used to distinguish between multiple geometry columns. If omitted, the first geometry column in the record will be determined. Conversely, passing the parameter will save column type lookups.

The maxdecimaldigits argument may be used to reduce the maximum number of decimal places used in output (defaults to 9). If you are using EPSG:4326 and are outputting the geometry only for display, maxdecimaldigits=6 can be a good choice for many maps.

The options argument can be used to add BBOX or CRS in GeoJSON output:

The id_column parameter is used to set the "id" member of the returned GeoJSON features. As per GeoJSON RFC, this SHOULD be used whenever a feature has a commonly used identifier, such as a primary key. When not specified, the produced features will not get an "id" member and any columns other than the geometry, including any potential keys, will just end up inside the feature’s "properties" member.

The GeoJSON specification states that polygons are oriented using the Right-Hand Rule, and some clients require this orientation. This can be ensured by using ST_ForcePolygonCCW . The specification also requires that geometry be in the WGS84 coordinate system (SRID = 4326). If necessary geometry can be projected into WGS84 using ST_Transform: ST_Transform( geom, 4326 ).

GeoJSON can be tested and viewed online at geojson.io and geojsonlint.com. It is widely supported by web mapping frameworks:

Availability: 1.3.4

Availability: 1.5.0 geography support was introduced.

Changed: 2.0.0 support default args and named args.

Changed: 3.0.0 support records as input

Changed: 3.0.0 output SRID if not EPSG:4326.

Changed: 3.5.0 allow specifying the column containing the feature id

This function supports 3d and will not drop the z-index.

Examples

Generate a FeatureCollection:

SELECT json_build_object(
    'type', 'FeatureCollection',
    'features', json_agg(ST_AsGeoJSON(t.*, id_column => 'id')::json)
    )
FROM ( VALUES (1, 'one', 'POINT(1 1)'::geometry),
              (2, 'two', 'POINT(2 2)'),
              (3, 'three', 'POINT(3 3)')
     ) as t(id, name, geom);

{"type" : "FeatureCollection", "features" : [{"type": "Feature", "geometry": {"type":"Point","coordinates":[1,1]}, "id": 1, "properties": {"name": "one"}}, {"type": "Feature", "geometry": {"type":"Point","coordinates":[2,2]}, "id": 2, "properties": {"name": "two"}}, {"type": "Feature", "geometry": {"type":"Point","coordinates":[3,3]}, "id": 3, "properties": {"name": "three"}}]}

Generate a Feature:

SELECT ST_AsGeoJSON(t.*, id_column => 'id')
FROM (VALUES (1, 'one', 'POINT(1 1)'::geometry)) AS t(id, name, geom);

                                                  st_asgeojson
-----------------------------------------------------------------------------------------------------------------
 {"type": "Feature", "geometry": {"type":"Point","coordinates":[1,1]}, "id": 1, "properties": {"name": "one"}}

Don't forget to transform your data to WGS84 longitude, latitude to conform with the GeoJSON specification:

SELECT ST_AsGeoJSON(ST_Transform(geom,4326)) from fe_edges limit 1;

					   st_asgeojson
-----------------------------------------------------------------------------------------------------------

{"type":"MultiLineString","coordinates":[[[-89.734634999999997,31.492072000000000],
[-89.734955999999997,31.492237999999997]]]}

3D geometries are supported:

SELECT ST_AsGeoJSON('LINESTRING(1 2 3, 4 5 6)');

{"type":"LineString","coordinates":[[1,2,3],[4,5,6]]}

See Also

ST_GeomFromGeoJSON, ST_ForcePolygonCCW , ST_Transform