# Studio Functions for Working with Geometries

Studio provides a set of functions for working with geometries.

| Function | Description |
| --- | --- |
| [`buffer()`](https://docs.foursquare.com/analytics-products/docs/expressions-geometric#buffer) | Creates a buffer polygon surrounding a point on the map. |
| [`bufferFeature()`](https://docs.foursquare.com/analytics-products/docs/expressions-geometric#bufferfeature) | Creates a buffer polygon surrounding a GeoJSON Geometry feature. |
| [`bufferH3()`](https://docs.foursquare.com/analytics-products/docs/expressions-geometric#bufferh3) | Creates a polygon surrounding an H3 cell. |
| [`centroid()`](https://docs.foursquare.com/analytics-products/docs/expressions-geometric#centroid) | Returns the center point of a GeoJSON Geometry feature. |
| [`latLngToPoint()`](https://docs.foursquare.com/analytics-products/docs/expressions-geometric#latLngToPoint) | Creates a GeoJSON Point from latitude/longitude coordinates. |
| [`pointLat()`](https://docs.foursquare.com/analytics-products/docs/expressions-geometric#pointlat) | Returns the latitude of a GeoJSON Point. |
| [`pointLng()`](https://docs.foursquare.com/analytics-products/docs/expressions-geometric#pointlng) | Returns the longitude of a GeoJSON Point. |

* * *

# buffer

Create buffer polygons surrounding each set of latitude/longitude coordinates.

### Method

JavaScript

```javascript
buffer(lat: number, lng: number, bufferDistance: number, distanceUnit?: string, pointsPerArc?: number): Feature
```

### Parameters

| Parameter | Type | Description |
| --- | --- | --- |
| `lat` | `number` | Required. A column containing latitude coordinates. |
| `lng` | `number` | Required. A column containing longitude coordinates. |
| `bufferDistance` | `number` | Required. The length of the buffer surrounding the point. |
| `distanceUnit` | `string` | The distance unit to use for the buffer, either `Meter`/`Meters`, or `Mile`/`Miles` (not case-sensitive). Default: `Mile` |
| `pointsPerArc` | `number` | The number of points to create the rounded corner of the buffered shape. A higher number of points generates a smoother buffer corner. Default: `10` |

### Returns

Returns a GeoJSON feature buffer for each set of coordinates.

### Example

Create a smoothed 40-meter buffer surrounding each point on the map:

JavaScript

```javascript
buffer(lat, lng, 40, "meter", 40);
```

* * *

# bufferFeature

Create buffer polygons surrounding a set of GeoJSON features/objects, such as polygons or multi-polygons.

### Method

JavaScript

```javascript
bufferFeature(feature: Feature, bufferDistance: number, distanceUnit?: string, pointsPerArc?: number): Feature
```

### Parameters

| Parameter | Type | Description |
| --- | --- | --- |
| `feature` | GeoJSON `feature` | Required. The name of the GeoJSON feature column to surround with buffer polygons. |
| `bufferDistance` | `number` | Required. The length of the buffer from the edge of each feature. |
| `distanceUnit` | `string` | The distance unit to use for the buffer, either `Meter`/`Meters`, or `Mile`/`Miles` (not case-sensitive). Default: `Mile` |
| `pointsPerArc` | `number` | The number of points to create the rounded corner of the buffered shape. A higher number of points generates a smoother buffer corner. Default: `10` |

### Returns

Returns a GeoJSON feature buffer for each existing GeoJSON feature.

### Example

Create a 50-meter buffer surrounding each road on the map:

JavaScript

```javascript
bufferFeature(roads, 50, "Meter");
```

* * *

# bufferH3

Create buffer polygons surrounding each H3 cell.

### Method

JavaScript

```javascript
bufferH3(h3: string, bufferDistance: number, distanceUnit?: string, pointsPerArc?: number): Feature
```

### Parameters

| Parameter | Type | Description |
| --- | --- | --- |
| `h3` | `string` | Required. A column containing H3 cell strings to surround with buffer polygons. |
| `bufferDistance` | `number` | Required. The length of the buffer from the edge of each cell. |
| `distanceUnit` | `string` | The distance unit to use for the buffer, either `Meter`/`Meters`, or `Mile`/`Miles` (not case-sensitive). Default: `Mile` |
| `pointsPerArc` | `number` | The number of points to create the rounded corner of the buffered shape. A higher number of points generates a smoother buffer corner. Default: `10` |

### Returns

Returns a GeoJSON feature buffer for each H3 cell.

### Example

Create a 2-mile buffer surrounding each H3 cell in `h3`:

JavaScript

```javascript
bufferh3(h3, 2);
```

* * *

# centroid

Get the centroid of a GeoJSON Geometry object. The geometry type could be `Point/MultiPoint`, `LineString/MultiLineString`, or `Polygon/MultiPolygon`. A geometry's geometric center of mass is computed and returned.

### Method

JavaScript

```javascript
centroid(geo: Feature): Feature<Point>
```

### Parameters

| Parameter | Type | Description |
| --- | --- | --- |
| `geo` | GeoJSON Geometry feature/object or a WKT `string`. | Required. The column containing the polygons to derive centroid from. |

### Returns

Returns a GeoJSON Point feature for each polygon provided.

### Example

Find the centroid for each GeoJSON Geometry feature/object in `_geojson`:

JavaScript

```javascript
centroid(_geojson);
```

* * *

# latLngToPoint

Creates a GeoJSON Point feature for each set of coordinates.

### Method

JavaScript

```javascript
latLngToPoint(lat: number, lng: number): Feature<Point>
```

### Parameters

| Parameter | Type | Description |
| --- | --- | --- |
| `lat` | `number` | Required. A column containing latitude coordinates. |
| `lng` | `number` | Required. A column containing longitude coordinates. |

### Returns

Returns a GeoJSON Point feature for each set of coordinates.

### Example

Create a GeoJSON Point feature for a set of coordinates:

JavaScript

```javascript
latLngToPoint(lat, lng);
```

* * *

# pointLat

Get the latitude value of a GeoJSON Point feature.

### Method

JavaScript

```javascript
pointLat(pt: Feature<Point>): number
```

### Parameters

| Parameter | Type | Description |
| --- | --- | --- |
| `pt` | A GeoJSON Point feature/object | Required. A column containing GeoJSON Points to derive latitude from. |

### Returns

Returns a numeric latitude value for each Point feature.

### Example

Retrieve the latitude values for each GeoJSON Point:

JavaScript

```javascript
pointLat(_geojson);
```

* * *

# pointLng

Get the longitude value of a GeoJSON Point feature.

### Method

JavaScript

```javascript
pointLng(pt: Feature<Point>): number
```

### Parameters

| Parameter | Type | Description |
| --- | --- | --- |
| `pt` | A GeoJSON Point feature/object | Required. A column containing GeoJSON Points to derive longitude from. |

### Returns

Returns a numeric longitude value for each Point feature.

### Example

Retrieve the longitude values for each GeoJSON Point:

JavaScript

```javascript
pointLng(_geojson);
```

> Note: `pointLat()` and `pointLng()` can be used to create new latitude and longitude columns for a Point layer.