# @turf/mask

# mask

Takes any type of [polygon](http://geojson.org/geojson-spec.html#polygon) and an optional mask and returns a [polygon](http://geojson.org/geojson-spec.html#polygon) exterior ring with holes.

**Parameters**

-   `polygon` **([FeatureCollection](http://geojson.org/geojson-spec.html#feature-collection-objects) \| [Feature](http://geojson.org/geojson-spec.html#feature-objects)<([Polygon](http://geojson.org/geojson-spec.html#polygon) \| [MultiPolygon](http://geojson.org/geojson-spec.html#multipolygon))>)** GeoJSON Polygon used as interior rings or holes.
-   `mask` **\[[Feature](http://geojson.org/geojson-spec.html#feature-objects)<[Polygon](http://geojson.org/geojson-spec.html#polygon)>]** GeoJSON Polygon used as the exterior ring (if undefined, the world extent is used)

**Examples**

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

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

//addToMap
var addToMap = [masked]
```

Returns **[Feature](http://geojson.org/geojson-spec.html#feature-objects)<[Polygon](http://geojson.org/geojson-spec.html#polygon)>** Masked Polygon (exterior ring with holes).

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---

This module is part of the [Turfjs project](http://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 module individually:

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

Or install the Turf module that includes it as a function:

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