@turf/union

union

Takes a collection of input polygons and returns a combined polygon. If the
input polygons are not contiguous, this function returns a multi-polygon
feature.

$3

* features [FeatureCollection][1]<([Polygon][2] | [MultiPolygon][3])> input polygon features
* options [Object][4] Optional Parameters (optional, default {})

* options.properties [GeoJsonProperties][5] properties to assign to output feature (optional, default {})

$3

``javascript
const poly1 = turf.polygon(
[
[
[-82.574787, 35.594087],
[-82.574787, 35.615581],
[-82.545261, 35.615581],
[-82.545261, 35.594087],
[-82.574787, 35.594087],
],
],
{ fill: "#0f0" }
);

const poly2 = turf.polygon(
[
[
[-82.560024, 35.585153],
[-82.560024, 35.602602],
[-82.52964, 35.602602],
[-82.52964, 35.585153],
[-82.560024, 35.585153],
],
],
);

const union = turf.union(turf.featureCollection([poly1, poly2]));

//addToMap
const addToMap = { poly1, poly2, union };

poly1.properties.fill = "#0f0";
poly2.properties.fill = "#00f";
union.properties.stroke = "red";
union.properties["stroke-width"] = 4;
union.properties.fill = "transparent";
`

Returns ([Feature][5]<([Polygon][2] | [MultiPolygon][3])> | null) a combined polygon or multi-polygon feature, or null if there were no input polygons to combine

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

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

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

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

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

---

This module is part of the Turfjs project, an open source module collection dedicated to geographic algorithms. It is maintained in the Turfjs/turf repository, where you can create PRs and issues.

$3

Install this single module individually:

`sh
$ npm install @turf/union
`

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

`sh
$ npm install @turf/turf
``