# @turf/mask

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## mask

Takes polygons or multipolygons and an optional mask, and returns an exterior
ring polygon with holes.

### Parameters

*   `polygon` **([Polygon][1] | [MultiPolygon][2] | [Feature][3]<([Polygon][1] | [MultiPolygon][2])> | [FeatureCollection][4]<([Polygon][1] | [MultiPolygon][2])>)** GeoJSON polygon used as interior rings or holes
*   `mask` **([Polygon][1] | [Feature][3]<[Polygon][1]>)?** GeoJSON polygon used as the exterior ring (if undefined, the world extent is used)
*   `options` **[Object][5]** Optional parameters (optional, default `{}`)

    *   `options.mutate` **[boolean][6]** allows the `mask` GeoJSON input to be mutated (performance improvement if true) (optional, default `false`)

### Examples

```javascript
const polygon = turf.polygon([[[112, -21], [116, -36], [146, -39], [153, -24], [133, -10], [112, -21]]]);
const mask = turf.polygon([[[90, -55], [170, -55], [170, 10], [90, 10], [90, -55]]]);

const masked = turf.mask(polygon, mask);

//addToMap
const addToMap = [masked]
```

Returns **[Feature][3]<[Polygon][1]>** Masked Polygon (exterior ring with holes)

[1]: https://tools.ietf.org/html/rfc7946#section-3.1.6

[2]: https://tools.ietf.org/html/rfc7946#section-3.1.7

[3]: https://tools.ietf.org/html/rfc7946#section-3.2

[4]: https://tools.ietf.org/html/rfc7946#section-3.3

[5]: https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Object

[6]: https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Boolean

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---

This module is part of the [Turfjs project](https://turfjs.org/), an open source module collection dedicated to geographic algorithms. It is maintained in the [Turfjs/turf](https://github.com/Turfjs/turf) repository, where you can create PRs and issues.

### Installation

Install this single module individually:

```sh
$ npm install @turf/mask
```

Or install the all-encompassing @turf/turf module that includes all modules as functions:

```sh
$ npm install @turf/turf
```