A MULTILINESTRING is a collection of LineStrings. MultiLineStrings are useful for gathering a group of LineStrings into one geometry. For example, you may want to gather the LineStrings denoting all of the roads in a particular municipality.
Examples
Well known text
A MultiLineString can be created from SQL by calling the st_geomfromtext function on a MultiLineString definition expressed in the Well Known Text (WKT) format.
SELECT ST_GeomFromText('MULTILINESTRING((0 0, 1440 900), (800 600, 200 400))');
st_geomfromtext
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
0105000000020000000102000000020000000000000000000000000000000000000000000000008096400000000000208C4001020000000200000000000000000089400000000000C0824000000000000069400000000000007940
(1 row)
SQL
A MultiLineString can be created from SQL by calling an aggregate function such as ST_Collect or ST_Union on a column that contains LineString geometries. In the example below, we will build a MultiLineString from several LineStrings.
First, insert the LineStrings:
CREATE TABLE tmp_linestrings (id INT8 default unique_rowid(), geom GEOMETRY);
INSERT INTO tmp_linestrings (geom)
VALUES
(st_geomfromtext('SRID=4326;LINESTRING(-88.243385 40.116421, -87.906471 43.038902, -95.992775 36.153980)')),
(st_geomfromtext('SRID=4326;LINESTRING(-75.704722 36.076944, -95.992775 36.153980, -87.906471 43.038902)')),
(st_geomfromtext('SRID=4326;LINESTRING(-76.8261 42.1727, -75.6608 41.4102,-73.5422 41.052, -73.929 41.707, -76.8261 42.1727)'));
Next, build a MultiLineString from the individual LineStrings using ST_Collect, and check the output with ST_GeometryType to verify that it is indeed a MultiLineString:
SELECT ST_GeometryType(st_collect(geom)) AS output FROM tmp_linestrings;
output
----------------------
ST_MultiLineString
(1 row)
Finally, drop the temporary table:
DROP TABLE tmp_linestrings;
See also
- Spatial objects
- POINT
- LINESTRING
- POLYGON
- MULTIPOINT
- MULTIPOLYGON
- GEOMETRYCOLLECTION
- Introducing Distributed Spatial Data in Free, Open Source CockroachDB (blog post)
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