# s2

Our S2 module is based on a port of the official S2 geometry library created by Google. For more information about S2 check the [library's website](http://s2geometry.io/) or the [Spatial Indexes section](https://docs.carto.com/data-and-analysis/analytics-toolbox-for-bigquery/key-concepts/spatial-indexes#s2) of this documentation.

## S2\_BOUNDARY <a href="#s2_boundary" id="s2_boundary"></a>

```sql
S2_BOUNDARY(id)
```

**Description**

Returns the boundary for a given S2 cell ID. We extract the boundary by getting the corner longitudes and latitudes, then enclose it in a GeoJSON and finally transform it into geography.

**Input parameters**

* `id`: `INT64` S2 cell ID to get the boundary geography from.

**Return type**

`GEOGRAPHY`

**Example**

{% tabs %}
{% tab title="carto-un" %}

```sql
SELECT `carto-un`.carto.S2_BOUNDARY(955378847514099712);
-- POLYGON((-3.41955272426037 40.25850071217, -3.41955272426037  ...
```

{% endtab %}

{% tab title="carto-un-eu" %}

```sql
SELECT `carto-un-eu`.carto.S2_BOUNDARY(955378847514099712);
-- POLYGON((-3.41955272426037 40.25850071217, -3.41955272426037  ...
```

{% endtab %}

{% tab title="manual" %}

```sql
SELECT carto.S2_BOUNDARY(955378847514099712);
-- POLYGON((-3.41955272426037 40.25850071217, -3.41955272426037  ...
```

{% endtab %}
{% endtabs %}

{% hint style="info" %}
S2 Cell edges are spherical geodesics. The boundary edges can be interpreted as straight lines in other GIS tools, so to export the exact shape of the cells, use `ST_GEOGFROM(ST_ASGEOJSON(geog)`. In this process, BigQuery will add intermediate points to preserve the geodesic curves.
{% endhint %}

## S2\_CENTER <a href="#s2_center" id="s2_center"></a>

```sql
S2_CENTER(id)
```

**Description**

Returns a POINT corresponding to the centroid of an S2 cell, given its ID.

**Input parameters**

* `id`: `INT64` S2 cell ID to get the boundary geography from.

**Return type**

`GEOGRAPHY`

**Example**

{% tabs %}
{% tab title="carto-un" %}

```sql
SELECT `carto-un`.carto.S2_CENTER(955378847514099712);
-- POINT(-3.58126923539589 40.4167087628243)
```

{% endtab %}

{% tab title="carto-un-eu" %}

```sql
SELECT `carto-un-eu`.carto.S2_CENTER(955378847514099712);
-- POINT(-3.58126923539589 40.4167087628243)
```

{% endtab %}

{% tab title="manual" %}

```sql
SELECT carto.S2_CENTER(955378847514099712);
-- POINT(-3.58126923539589 40.4167087628243)
```

{% endtab %}
{% endtabs %}

## S2\_FROMGEOGPOINT <a href="#s2_fromgeogpoint" id="s2_fromgeogpoint"></a>

```sql
S2_FROMGEOGPOINT(point, resolution)
```

**Description**

Returns the S2 cell ID of a given point at a requested resolution.

**Input parameters**

* `point`: `GEOGRAPHY` point to get the ID from.
* `resolution`: `INT64` level of detail or zoom.

**Return type**

`INT64`

**Example**

{% tabs %}
{% tab title="carto-un" %}

```sql
SELECT `carto-un`.carto.S2_FROMGEOGPOINT(ST_GEOGPOINT(-3.7038, 40.4168), 8);
-- 955378847514099712
```

{% endtab %}

{% tab title="carto-un-eu" %}

```sql
SELECT `carto-un-eu`.carto.S2_FROMGEOGPOINT(ST_GEOGPOINT(-3.7038, 40.4168), 8);
-- 955378847514099712
```

{% endtab %}

{% tab title="manual" %}

```sql
SELECT carto.S2_FROMGEOGPOINT(ST_GEOGPOINT(-3.7038, 40.4168), 8);
-- 955378847514099712
```

{% endtab %}
{% endtabs %}

## S2\_FROMHILBERTQUADKEY <a href="#s2_fromhilbertquadkey" id="s2_fromhilbertquadkey"></a>

```sql
S2_FROMHILBERTQUADKEY(hquadkey)
```

**Description**

Returns the conversion of a Hilbert quadkey (a.k.a Hilbert curve quadtree ID) into a S2 cell ID.

**Input parameters**

* `hquadkey`: `STRING` Hilbert quadkey to be converted.

**Return type**

`INT64`

**Example**

{% tabs %}
{% tab title="carto-un" %}

```sql
SELECT `carto-un`.carto.S2_FROMHILBERTQUADKEY('0/12220101');
-- 955378847514099712
```

{% endtab %}

{% tab title="carto-un-eu" %}

```sql
SELECT `carto-un-eu`.carto.S2_FROMHILBERTQUADKEY('0/12220101');
-- 955378847514099712
```

{% endtab %}

{% tab title="manual" %}

```sql
SELECT carto.S2_FROMHILBERTQUADKEY('0/12220101');
-- 955378847514099712
```

{% endtab %}
{% endtabs %}

## S2\_FROMLONGLAT <a href="#s2_fromlonglat" id="s2_fromlonglat"></a>

```sql
S2_FROMLONGLAT(longitude, latitude, resolution)
```

**Description**

Returns the S2 cell ID for a given longitude, latitude and zoom resolution.

**Input parameters**

* `longitude`: `FLOAT64` horizontal coordinate on the map.
* `latitude`: `FLOAT64` vertical coordinate on the map.
* `resolution`: `INT64` level of detail or zoom.

**Return type**

`INT64`

**Example**

{% tabs %}
{% tab title="carto-un" %}

```sql
SELECT `carto-un`.carto.S2_FROMLONGLAT(-3.7038, 40.4168, 8);
-- 955378847514099712
```

{% endtab %}

{% tab title="carto-un-eu" %}

```sql
SELECT `carto-un-eu`.carto.S2_FROMLONGLAT(-3.7038, 40.4168, 8);
-- 955378847514099712
```

{% endtab %}

{% tab title="manual" %}

```sql
SELECT carto.S2_FROMLONGLAT(-3.7038, 40.4168, 8);
-- 955378847514099712
```

{% endtab %}
{% endtabs %}

## S2\_FROMTOKEN <a href="#s2_fromtoken" id="s2_fromtoken"></a>

```sql
S2_FROMTOKEN(token)
```

**Description**

Returns the conversion of a token into a S2 cell ID.

**Input parameters**

* `token`: `STRING` S2 cell hexified ID.

**Return type**

`INT64`

**Example**

{% tabs %}
{% tab title="carto-un" %}

```sql
SELECT `carto-un`.carto.S2_FROMTOKEN('0d423');
-- 955378847514099712
```

{% endtab %}

{% tab title="carto-un-eu" %}

```sql
SELECT `carto-un-eu`.carto.S2_FROMTOKEN('0d423');
-- 955378847514099712
```

{% endtab %}

{% tab title="manual" %}

```sql
SELECT carto.S2_FROMTOKEN('0d423');
-- 955378847514099712
```

{% endtab %}
{% endtabs %}

## S2\_FROMUINT64REPR <a href="#s2_fromuint64repr" id="s2_fromuint64repr"></a>

```sql
S2_FROMUINT64REPR(uid)
```

**Description**

Returns the cell ID from a UINT64 representation.

**Input parameters**

* `uid`: `STRING` UINT64 representation of a S2 cell ID.

**Return type**

`INT64`

**Example**

{% tabs %}
{% tab title="carto-un" %}

```sql
SELECT `carto-un`.carto.S2_FROMUINT64REPR('9926595690882924544');
-- -8520148382826627072
```

{% endtab %}

{% tab title="carto-un-eu" %}

```sql
SELECT `carto-un-eu`.carto.S2_FROMUINT64REPR('9926595690882924544');
-- -8520148382826627072
```

{% endtab %}

{% tab title="manual" %}

```sql
SELECT carto.S2_FROMUINT64REPR('9926595690882924544');
-- -8520148382826627072
```

{% endtab %}
{% endtabs %}

## S2\_RESOLUTION <a href="#s2_resolution" id="s2_resolution"></a>

```sql
S2_RESOLUTION(index)
```

**Description**

Returns the S2 cell resolution as an integer.

**Input parameters**

* `index`: `STRING` The S2 cell index.

**Return type**

`INT64`

**Example**

{% tabs %}
{% tab title="carto-un" %}

```sql
SELECT `carto-un`.carto.S2_RESOLUTION(955378847514099712);
-- 9
```

{% endtab %}

{% tab title="carto-un-eu" %}

```sql
SELECT `carto-un-eu`.carto.S2_RESOLUTION(955378847514099712);
-- 9
```

{% endtab %}

{% tab title="manual" %}

```sql
SELECT carto.S2_RESOLUTION(955378847514099712);
-- 9
```

{% endtab %}
{% endtabs %}

## S2\_TOCHILDREN <a href="#s2_tochildren" id="s2_tochildren"></a>

```sql
S2_TOCHILDREN(index, resolution)
```

**Description**

Returns an array with the S2 indexes of the children/descendents of the given hexagon at the given resolution.

**Input parameters**

* `index`: `STRING` The S2 cell index.
* `resolution`: `INT64` number between 0 and 30 with the [S2 resolution](https://S2geo.org/docs/core-library/restable).

**Return type**

`ARRAY<STRING>`

**Example**

{% tabs %}
{% tab title="carto-un" %}

```sql
SELECT `carto-un`.carto.S2_TOCHILDREN(955378847514099712, 10);
-- 955365653374566400
-- 955374449467588608
-- 955383245560610816
-- 955392041653633024
```

{% endtab %}

{% tab title="carto-un-eu" %}

```sql
SELECT `carto-un-eu`.carto.S2_TOCHILDREN(955378847514099712, 10);
-- 955365653374566400
-- 955374449467588608
-- 955383245560610816
-- 955392041653633024
```

{% endtab %}

{% tab title="manual" %}

```sql
SELECT carto.S2_TOCHILDREN(955378847514099712, 10);
-- 955365653374566400
-- 955374449467588608
-- 955383245560610816
-- 955392041653633024
```

{% endtab %}
{% endtabs %}

## S2\_TOHILBERTQUADKEY <a href="#s2_tohilbertquadkey" id="s2_tohilbertquadkey"></a>

```sql
S2_TOHILBERTQUADKEY(id)
```

**Description**

Returns the conversion of a S2 cell ID into a Hilbert quadkey (a.k.a Hilbert curve quadtree ID).

**Input parameters**

* `id`: `INT64` S2 cell ID to be converted.

**Return type**

`STRING`

**Example**

{% tabs %}
{% tab title="carto-un" %}

```sql
SELECT `carto-un`.carto.S2_TOHILBERTQUADKEY(955378847514099712);
-- 0/12220101
```

{% endtab %}

{% tab title="carto-un-eu" %}

```sql
SELECT `carto-un-eu`.carto.S2_TOHILBERTQUADKEY(955378847514099712);
-- 0/12220101
```

{% endtab %}

{% tab title="manual" %}

```sql
SELECT carto.S2_TOHILBERTQUADKEY(955378847514099712);
-- 0/12220101
```

{% endtab %}
{% endtabs %}

## S2\_TOTOKEN <a href="#s2_totoken" id="s2_totoken"></a>

```sql
S2_TOTOKEN(id)
```

**Description**

Returns the conversion of a S2 cell ID into a token (S2 cell hexified ID).

**Input parameters**

* `id`: `INT64` S2 cell ID.

**Return type**

`STRING`

**Example**

{% tabs %}
{% tab title="carto-un" %}

```sql
SELECT `carto-un`.carto.S2_TOTOKEN(955378847514099712);
-- 0d423
```

{% endtab %}

{% tab title="carto-un-eu" %}

```sql
SELECT `carto-un-eu`.carto.S2_TOTOKEN(955378847514099712);
-- 0d423
```

{% endtab %}

{% tab title="manual" %}

```sql
SELECT carto.S2_TOTOKEN(955378847514099712);
-- 0d423
```

{% endtab %}
{% endtabs %}

## S2\_TOUINT64REPR <a href="#s2_touint64repr" id="s2_touint64repr"></a>

```sql
S2_TOUINT64REPR(id)
```

**Description**

Returns the UINT64 representation of a cell ID.

**Input parameters**

* `id`: `INT64` S2 cell ID.

**Return type**

`STRING`

**Example**

{% tabs %}
{% tab title="carto-un" %}

```sql
SELECT `carto-un`.carto.S2_TOUINT64REPR(-8520148382826627072);
-- 9926595690882924544
```

{% endtab %}

{% tab title="carto-un-eu" %}

```sql
SELECT `carto-un-eu`.carto.S2_TOUINT64REPR(-8520148382826627072);
-- 9926595690882924544
```

{% endtab %}

{% tab title="manual" %}

```sql
SELECT carto.S2_TOUINT64REPR(-8520148382826627072);
-- 9926595690882924544
```

{% endtab %}
{% endtabs %}

<img src="/files/4m1BK9j4Wq34gat4HHd2" alt="EU flag" data-size="line">This project has received funding from the [European Union’s Horizon 2020](https://ec.europa.eu/programmes/horizon2020/en) research and innovation programme under grant agreement No 960401.


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://docs.carto.com/data-and-analysis/analytics-toolbox-for-bigquery/sql-reference/s2.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.