Convex hull
The smallest convex polygon that fully contains a geometry (think: a tight rubber band around it).
Category: Geometry · Also known as: minimum convex polygon, convex hull polygon, ST_ConvexHull
Definition (expanded)
A convex hull is a simplified outline with no inward dents. It is often used for quick approximations, coarse filtering, or as a first-pass shape for analysis. Convex hulls ignore holes and concavities by design, so they can overestimate area for concave shapes.
Examples
PostGIS convex hull
SQL
SELECT ST_AsText(ST_ConvexHull(geom)) FROM my_table;
Common mistakes
- Assuming the hull matches the original boundary (it will fill in concave dents).
- Using convex hull area as a proxy for the true polygon area.
Related terms
PolygonA closed area geometry defined by an exterior ring and optional interior rings (holes).MultiPolygonA geometry containing multiple polygons (parts), each with its own exterior ring and optional holes.Bounding Box (BBox)A rectangle that fully contains a geometry, usually represented as [minX, minY, maxX, maxY].SimplifyReduces vertex count while approximating the shape to improve performance and reduce file size.