# @turf/tag

# tag

Takes a set of [points](http://geojson.org/geojson-spec.html#point) and a set of [polygons](http://geojson.org/geojson-spec.html#polygon) and performs a spatial join.

**Parameters**

-   `points` **[FeatureCollection](http://geojson.org/geojson-spec.html#feature-collection-objects)<[Point](http://geojson.org/geojson-spec.html#point)>** input points
-   `polygons` **[FeatureCollection](http://geojson.org/geojson-spec.html#feature-collection-objects)<[Polygon](http://geojson.org/geojson-spec.html#polygon)>** input polygons
-   `field` **[string](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String)** property in `polygons` to add to joined {<Point>} features
-   `outField` **[string](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String)** property in `points` in which to store joined property from `polygons`

**Examples**

```javascript
var pt1 = turf.point([-77, 44]);
var pt2 = turf.point([-77, 38]);
var poly1 = turf.polygon([[
  [-81, 41],
  [-81, 47],
  [-72, 47],
  [-72, 41],
  [-81, 41]
]], {pop: 3000});
var poly2 = turf.polygon([[
  [-81, 35],
  [-81, 41],
  [-72, 41],
  [-72, 35],
  [-81, 35]
]], {pop: 1000});

var points = turf.featureCollection([pt1, pt2]);
var polygons = turf.featureCollection([poly1, poly2]);

var tagged = turf.tag(points, polygons, 'pop', 'population');

//addToMap
var addToMap = [tagged, polygons]
```

Returns **[FeatureCollection](http://geojson.org/geojson-spec.html#feature-collection-objects)&lt;[Point](http://geojson.org/geojson-spec.html#point)>** points with `containingPolyId` property containing values from `polyId`

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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/tag
```

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

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