docs/api/sql/geography/Geography-Functions/ST_Centroid.md

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# ST_Centroid

Introduction: Returns the spherical centroid of a geography as a Geography point, computed on the sphere using S2:

- **Polygon / MultiPolygon** — area-weighted centroid via `S2Polygon.getCentroid()`.
- **LineString / MultiLineString** — length-weighted centroid via `S2Polyline.getCentroid()`.
- **Point / MultiPoint** — mean of the unit vectors.
- **GeographyCollection** — recursive weighted sum across the children.

The result is the unit-length centroid on the sphere. Unlike a planar (lon/lat) centroid, it is correct for antimeridian-crossing and high-latitude geographies. As with JTS for non-convex shapes, the centroid may lie outside the input geometry. Returns `NULL` when the centroid is undefined (empty geometry, or antipodal points whose unit vectors cancel).

Format:

`ST_Centroid (A: Geography)`

Return type: `Geography`

Since: `v1.9.1`

SQL Example

```sql
SELECT ST_AsEWKT(ST_Centroid(ST_GeogFromWKT('POLYGON ((0 0, 2 0, 2 2, 0 2, 0 0))')));
```

Output (small `O(d²/R²)` spherical correction vs the planar `(1 1)`):

```
POINT (1 1)
```

For an antimeridian-crossing polygon, the spherical centroid stays on the antimeridian instead of jumping to the opposite side of the planet, which a planar centroid would do:

```sql
SELECT ST_AsEWKT(ST_Centroid(ST_GeogFromWKT('POLYGON ((170 -1, -170 -1, -170 1, 170 1, 170 -1))')));
-- result: POINT near (180, 0) (or (-180, 0)), NOT (0, 0)
```