STIntersects

STIntersects is a spatial predicate used in geographic information systems to determine whether two geometries share any portion of space. The predicate is part of the OpenGIS Simple Features specification and is implemented in many GIS libraries and databases, including PostGIS, SpatiaLite, GEOS-based tools, and related bindings. In practice, STIntersects tests whether the intersection of the two input geometries is non-empty.

Semantics and behavior

STIntersects returns a boolean value: true if the two geometries have at least one point in common, including shared boundary points, edges, or overlapping areas. It returns false if the geometries do not touch or overlap at any point. If either input is NULL, the result is typically NULL in most database implementations. If either geometry is empty, the intersection is empty, and the function returns false.

Spatial relationships

STIntersects is a broad predicate: it is true for intersecting points, lines, and polygons, regardless of geometry dimension. It is symmetric, so STIntersects(A, B) is equivalent to STIntersects(B, A). It is distinct from other spatial predicates such as STContains, STWithin, STOverlaps, STTouches, and STDisjoint, each expressing a different form of spatial relationship.

Performance considerations

Queries using STIntersects often benefit from spatial indexes (for example, GiST indexes in PostgreSQL/PostGIS). A typical pattern uses a bounding-box pre-filter (the && operator) before applying STIntersects to reduce the number of candidate pairs and improve performance.

Examples

STIntersects(POINT(0 0), LINESTRING(0 0, 1 1)) yields true. STIntersects(POINT(0 0), POLYGON(10 10, 20 10, 20 20, 10 20)) yields false. STIntersects(MULTIPOLYGON(...), POLYGON(...)) yields true if any area overlaps or touches.