Name

ST_AsGeoJSON — Return a geometry as a GeoJSON element.

Synopsis

text ST_AsGeoJSON(record feature, text geomcolumnname, integer maxdecimaldigits=9, boolean pretty_bool=false);

text ST_AsGeoJSON(geometry geom, integer maxdecimaldigits=9, integer options=8);

text ST_AsGeoJSON(geography geog, integer maxdecimaldigits=9, integer options=0);

Description

Returns a geometry as a GeoJSON "geometry", or a row as a GeoJSON "feature". (See the GeoJSON specifications RFC 7946). 2D and 3D Geometries are both supported. GeoJSON only support SFS 1.1 geometry types (no curve support for example).

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:

  • 0: means no option

  • 1: GeoJSON BBOX

  • 2: GeoJSON Short CRS (e.g EPSG:4326)

  • 4: GeoJSON Long CRS (e.g urn:ogc:def:crs:EPSG::4326)

  • 8: GeoJSON Short CRS if not EPSG:4326 (default)

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.

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

Generate a Feature:

SELECT ST_AsGeoJSON(t.*)
FROM (VALUES (1, 'one', 'POINT(1 1)'::geometry)) AS t(id, name, geom);
                                                  st_asgeojson
-----------------------------------------------------------------------------------------------------------------
 {"type": "Feature", "geometry": {"type":"Point","coordinates":[1,1]}, "properties": {"id": 1, "name": "one"}}

An alternate way to generate Features with an id property is to use JSONB functions and operators:

SELECT jsonb_build_object(
    'type',       'Feature',
    'id',         id,
    'geometry',   ST_AsGeoJSON(geom)::jsonb,
    'properties', to_jsonb( t.* ) - 'id' - 'geom'
    ) AS json
FROM (VALUES (1, 'one', 'POINT(1 1)'::geometry)) AS t(id, name, geom);
                                                  json
-----------------------------------------------------------------------------------------------------------------
 {"id": 1, "type": "Feature", "geometry": {"type": "Point", "coordinates": [1, 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