Skip to main content

ST_Intersection

Returns the intersection (shared area) of two geometries.

Syntax​

ST_Intersection(geometry_a, geometry_b)

Parameters​

ParameterTypeDescription
geometry_aGeometryFirst geometry
geometry_bGeometrySecond geometry

Returns​

TypeDescription
Binary (WKB)Intersection geometry as WKB with geoarrow.wkb metadata

Examples​

Intersection of Overlapping Polygons​

SELECT ST_Intersection(
    ST_GeomFromText('POLYGON((0 0, 2 0, 2 2, 0 2, 0 0))'),
    ST_GeomFromText('POLYGON((1 1, 3 1, 3 3, 1 3, 1 1))')
);
-- Returns: POLYGON((1 1, 2 1, 2 2, 1 2, 1 1))

Clip Features to Boundary​

SELECT id, ST_Intersection(feature.geom, boundary.geom) as clipped
FROM features feature, boundaries boundary
WHERE boundary.name = 'Study Area'
  AND ST_Intersects(feature.geom, boundary.geom);

Calculate Overlap Area​

SELECT
    a.id as parcel_a,
    b.id as parcel_b,
    ST_Area(ST_Intersection(a.geom, b.geom)) as overlap_area
FROM parcels a, parcels b
WHERE a.id < b.id
  AND ST_Intersects(a.geom, b.geom);

Line-Polygon Intersection​

SELECT ST_Intersection(
    ST_GeomFromText('LINESTRING(0 0, 10 10)'),
    ST_GeomFromText('POLYGON((2 2, 8 2, 8 8, 2 8, 2 2))')
);
-- Returns: LINESTRING(2 2, 8 8) - portion of line inside polygon

Notes​

  • Returns empty geometry if no intersection exists
  • Result type depends on intersection geometry (point, line, or polygon)
  • Always check ST_Intersects first for better performance
  • Useful for clipping features to study areas

See Also​