# supercluster [![Simply Awesome](https://img.shields.io/badge/simply-awesome-brightgreen.svg)](https://github.com/mourner/projects) [![Build Status](https://travis-ci.com/mapbox/supercluster.svg?branch=main)](https://travis-ci.com/mapbox/supercluster)

A very fast JavaScript library for geospatial point clustering for browsers and Node.

```js
const index = new Supercluster({radius: 40, maxZoom: 16});
index.load(points);

const clusters = index.getClusters([-180, -85, 180, 85], 2);
```

Clustering 6 million points in Leaflet:

![clustering demo on an interactive Leaflet map](https://cloud.githubusercontent.com/assets/25395/11857351/43407b46-a40c-11e5-8662-e99ab1cd2cb7.gif)

Supercluster was built to power clustering in [Mapbox GL JS](https://www.mapbox.com/mapbox-gljs). Read about how it works [on the Mapbox blog](https://blog.mapbox.com/clustering-millions-of-points-on-a-map-with-supercluster-272046ec5c97).

## Install

Install using NPM (`npm install supercluster`) or Yarn (`yarn add supercluster`), then:

```js
// import as a ES module in Node
import Supercluster from 'supercluster';

// import from a CDN in the browser:
import Supercluster from 'https://esm.run/supercluster';
```

Or use it with an ordinary script tag in the browser:

```html
<script src="https://unpkg.com/supercluster@8.0.0/dist/supercluster.min.js"></script>
```

## Methods

#### `load(points)`

Loads an array of [GeoJSON Feature](https://tools.ietf.org/html/rfc7946#section-3.2) objects. Each feature's `geometry` must be a [GeoJSON Point](https://tools.ietf.org/html/rfc7946#section-3.1.2). Once loaded, index is immutable.

#### `getClusters(bbox, zoom)`

For the given `bbox` array (`[westLng, southLat, eastLng, northLat]`) and integer `zoom`, returns an array of clusters and points as [GeoJSON Feature](https://tools.ietf.org/html/rfc7946#section-3.2) objects.

#### `getTile(z, x, y)`

For a given zoom and x/y coordinates, returns a [geojson-vt](https://github.com/mapbox/geojson-vt)-compatible JSON tile object with cluster/point features.

#### `getChildren(clusterId)`

Returns the children of a cluster (on the next zoom level) given its id (`cluster_id` value from feature properties).

#### `getLeaves(clusterId, limit = 10, offset = 0)`

Returns all the points of a cluster (given its `cluster_id`), with pagination support:
`limit` is the number of points to return (set to `Infinity` for all points),
and `offset` is the amount of points to skip (for pagination).

#### `getClusterExpansionZoom(clusterId)`

Returns the zoom on which the cluster expands into several children (useful for "click to zoom" feature) given the cluster's `cluster_id`.

## Options

| Option     | Default | Description                                                       |
|------------|---------|-------------------------------------------------------------------|
| minZoom    | 0       | Minimum zoom level at which clusters are generated.               |
| maxZoom    | 16      | Maximum zoom level at which clusters are generated.               |
| minPoints  | 2       | Minimum number of points to form a cluster.                       |
| radius     | 40      | Cluster radius, in pixels.                                        |
| extent     | 512     | (Tiles) Tile extent. Radius is calculated relative to this value. |
| nodeSize   | 64      | Size of the KD-tree leaf node. Affects performance.               |
| log        | false   | Whether timing info should be logged.                             |
| generateId | false   | Whether to generate ids for input features in vector tiles.       |

### Property map/reduce options

In addition to the options above, Supercluster supports property aggregation with the following two options:

- `map`: a function that returns cluster properties corresponding to a single point.
- `reduce`: a reduce function that merges properties of two clusters into one.

Example of setting up a `sum` cluster property that accumulates the sum of `myValue` property values:

```js
const index = new Supercluster({
    map: (props) => ({sum: props.myValue}),
    reduce: (accumulated, props) => { accumulated.sum += props.sum; }
});
```

The `map`/`reduce` options must satisfy these conditions to work correctly:

- `map` must return a new object, not existing `properties` of a point, otherwise it will get overwritten.
- `reduce` must not mutate the second argument (`props`).

## TypeScript

Install `@types/supercluster` for the TypeScript type definitions:

```
npm install @types/supercluster --save-dev 
```

## Developing Supercluster

```
npm install       # install dependencies
npm run build     # generate dist/supercluster.js and dist/supercluster.min.js
npm test          # run tests
```