Name
ST_AsGeoJSON — Return the geometry as a GeoJSON element.
Synopsis
text ST_AsGeoJSON(geometry geom, integer maxdecimaldigits=15, integer options=0);
text ST_AsGeoJSON(geography geog, integer maxdecimaldigits=15, integer options=0);
text ST_AsGeoJSON(integer gj_version, geometry geom, integer maxdecimaldigits=15, integer options=0);
text ST_AsGeoJSON(integer gj_version, geography geog, integer maxdecimaldigits=15, integer options=0);
Description
Return the geometry as a GeoJSON element. (Cf GeoJSON specifications 1.0). 2D and 3D Geometries are both supported. GeoJSON only support SFS 1.1 geometry type (no curve support for example).
The gj_version parameter is the major version of the GeoJSON spec. If specified, must be 1. This represents the spec version of GeoJSON.
The third argument may be used to reduce the maximum number of decimal places used in output (defaults to 15). 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 last options argument could be used to add BBOX or CRS in GeoJSON output:
0: means no option (default value)
1: GeoJSON BBOX
2: GeoJSON Short CRS (e.g EPSG:4326)
4: GeoJSON Long CRS (e.g urn:ogc:def:crs:EPSG::4326)
Version 1: ST_AsGeoJSON(geom) / maxdecimaldigits=15 version=1 options=0
Version 2: ST_AsGeoJSON(geom, maxdecimaldigits) / version=1 options=0
Version 3: ST_AsGeoJSON(geom, maxdecimaldigits, options) / version=1
Version 4: ST_AsGeoJSON(gj_version, geom) / maxdecimaldigits=15 options=0
Version 5: ST_AsGeoJSON(gj_version, geom, maxdecimaldigits) / options=0
Version 6: ST_AsGeoJSON(gj_version, geom, maxdecimaldigits, options)
Availability: 1.3.4
Availability: 1.5.0 geography support was introduced.
Changed: 2.0.0 support default args and named args.
This function supports 3d and will not drop the z-index.
Examples
GeoJSON format is popular among web mapping frameworks.
You can test and view your GeoJSON data online on geojson.io.
ST_AsGeoJSON only builds geometry. You need to build the rest of Feature from your Postgres table yourself:
select row_to_json(fc)
from (
select
'FeatureCollection' as "type",
array_to_json(array_agg(f)) as "features"
from (
select
'Feature' as "type",
ST_AsGeoJSON(ST_Transform(way, 4326), 6) :: json as "geometry",
(
select json_strip_nulls(row_to_json(t))
from (
select
osm_id,
"natural",
place
) t
) as "properties"
from planet_osm_point
where
"natural" is not null
or place is not null
limit 10
) as f
) as fc;
st_asgeojson
-----------------------------------------------------------------------------------------------------------
{"type":"FeatureCollection","features":[{"type":"Feature","geometry":{"type":"Point","coordinates":[23.569251,51.541599]},"properties":{"osm_id":3424148658,"place":"locality"}},{"type":"Feature","geometry":{"type":"Point","coordinates":[23.625174,51.511718]},"properties":{"osm_id":4322036818,"place":"locality"}},{"type":"Feature","geometry":{"type":"Point","coordinates":[23.613928,51.5417]},"properties":{"osm_id":242979330,"place":"hamlet"}},{"type":"Feature","geometry":{"type":"Point","coordinates":[23.586361,51.563272]},"properties":{"osm_id":3424148656,"place":"locality"}},{"type":"Feature","geometry":{"type":"Point","coordinates":[23.605488,51.553886]},"properties":{"osm_id":242979323,"place":"village"}},{"type":"Feature","geometry":{"type":"Point","coordinates":[23.6067,51.57609]},"properties":{"osm_id":242979327,"place":"village"}},{"type":"Feature","geometry":{"type":"Point","coordinates":[23.636533,51.575683]},"properties":{"osm_id":5737800420,"place":"locality"}},{"type":"Feature","geometry":{"type":"Point","coordinates":[23.656733,51.518733]},"properties":{"osm_id":5737802397,"place":"locality"}},{"type":"Feature","geometry":{"type":"Point","coordinates":[23.672542,51.504584]},"properties":{"osm_id":242979320,"place":"hamlet"}},{"type":"Feature","geometry":{"type":"Point","coordinates":[23.574094,51.63389]},"properties":{"osm_id":242979333,"place":"village"}}]}
SELECT ST_AsGeoJSON(geom) from fe_edges limit 1;
st_asgeojson
-----------------------------------------------------------------------------------------------------------
{"type":"MultiLineString","coordinates":[[[-89.734634999999997,31.492072000000000],
[-89.734955999999997,31.492237999999997]]]}
(1 row)You can also use it with 3D geometries:
SELECT ST_AsGeoJSON('LINESTRING(1 2 3, 4 5 6)');
st_asgeojson
-----------------------------------------------------------------------------------------
{"type":"LineString","coordinates":[[1,2,3],[4,5,6]]}