A POLYGON is a shape with a closed exterior that is made up of lines. Polygons can also contain holes. Polygons are often used to represent areas such as countries, states, or municipalities.
The coordinates of each Point and line that make up the Polygon are translated according to the current spatial reference system (denoted by an SRID) to determine what the point "is", or what it "means" relative to the other spatial objects (if any) in the data set.
Examples
Well known text
A Polygon can be created from SQL by calling the st_geomfromtext function on a LineString definition expressed in the Well Known Text (WKT) format as shown below.
SELECT ST_GeomFromText('POLYGON((0 0, 0 1024, 1024 1024, 1024 0, 0 0))');
st_geomfromtext
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
010300000001000000050000000000000000000000000000000000000000000000000000000000000000009040000000000000904000000000000090400000000000009040000000000000000000000000000000000000000000000000
(1 row)
Polygons with holes
To represent a polygon with holes in WKT, add one or more additional lists of coordinates that define the boundaries of the holes as shown below:
SELECT ST_GeomFromText('POLYGON((-87.906471 43.038902, -95.992775 36.153980, -75.704722 36.076944, -87.906471 43.038902), (-87.623177 41.881832, -90.199402 38.627003, -82.446732 38.413651, -87.623177 41.881832))');
st_geomfromtext
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
010300000002000000040000006FF1F09E03FA55C0DFDFA0BDFA844540545227A089FF57C0791EDC9DB513424064B14D2A1AED52C0CCCF0D4DD90942406FF1F09E03FA55C0DFDFA0BDFA84454004000000A4A7C821E2E755C07C48F8DEDFF0444073309B00C38C56C038BF61A241504340E884D041979C54C0967A1684F2344340A4A7C821E2E755C07C48F8DEDFF04440
(1 row)
Using a SQL function
You can also use the st_makepolygon function on a LineString that defines the outer boundary of the Polygon, e.g.:
SELECT ST_MakePolygon('LINESTRING(0 0, 0 1024, 1024 1024, 1024 0, 0 0)');
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
010300000001000000050000000000000000000000000000000000000000000000000000000000000000009040000000000000904000000000000090400000000000009040000000000000000000000000000000000000000000000000
(1 row)
See also
- Spatial objects
- POINT
- LINESTRING
- MULTIPOINT
- MULTILINESTRING
- MULTIPOLYGON
- GEOMETRYCOLLECTION
- Introducing Distributed Spatial Data in Free, Open Source CockroachDB (blog post)
Was this helpful?
