# Geographic distances

`great_circle_distance` calculates the shortest spherical surface distance between two longitude/latitude positions. It returns metres using a sphere with radius 6,371,000 metres.

The result describes a geographic arc, rather than a road route or an ellipsoidal distance.

## Syntax

```text
great_circle_distance(longitude1, latitude1, longitude2, latitude2)
```

## Arguments

Longitudes are in degrees from -180 through 180. Latitudes are in degrees from -90 through 90. Coordinates must satisfy those ranges; SQL NULL propagates.

## Returned value

An approximate floating-point distance in metres. Identical positions return zero.

## Examples

### One degree north along a meridian

```sql
SELECT round(great_circle_distance(0, 0, 0, 1)) AS metres
FORMAT csv;
```

```text
111195.0
```

### Identical positions

```sql
SELECT great_circle_distance(10, 20, 10, 20)
FORMAT csv;
```

```text
0.0
```

See [geometry construction](https://coordinatordb.com/docs/reference/functions/regular-functions/geo/geometry) for typed coordinate collections.