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Author message:

This package has been moved to @sintef/prune-cluster


2.1.0 • Public • Published


PruneCluster is a fast and realtime marker clustering library.

It's working with Leaflet as an alternative to Leaflet.markercluster.

The library is designed for large datasets or live situations. The memory consumption is kept low and the library is fast on mobile devices, thanks to a new algorithm inspired by collision detection in physical engines.

Example: Realtime clusters of tweets.



The clusters can be updated in realtime. It's perfect for live situations.


Number of markers First step Update (low zoom level) Update (high zoom level)
100 instant instant instant
1 000 instant instant instant
10 000 14ms 3ms 2ms
60 000 70ms 23ms 9ms
150 000 220ms 60ms 20ms
1 000 000 1.9s 400ms 135ms

These values are tested with random positions, on a recent laptop, using Chrome 38. One half of markers is moving randomly and the other half is static. It is also fast enough for mobile devices.

If you prefer real world data, the 50k Leaflet.markercluster example is computed in 60ms (original).


You can specify the weight of each marker.

For example, you may want to add more importance to a marker representing an incident, than a marker representing a tweet.


You can specify a category for the markers. Then a small object representing the number of markers for each category is attached to the clusters. This way, you can create cluster icons adapted to their content.

Dynamic cluster size

The size of a cluster can be adjusted on the fly (Example)


The markers can be filtered easily with no performance cost.


    <!-- In <head> -->
    <link rel="stylesheet" href=""/>
    <!-- In <head> or before </body> -->
    <script src=""></script> 
    <script src="PruneCluster/dist/PruneCluster.js"></script> 
var pruneCluster = new PruneClusterForLeaflet();
var marker = new PruneCluster.Marker(latitude, longitude);

PruneClusterForLeaflet constructor

PruneClusterForLeaflet(size, margin)

You can specify the size and margin which affect when your clusters and markers will be merged.

size defaults to 120 and margin to 20.

Update a position

marker.Move(lat, lng);


// Remove all the markers
// Remove a list of markers

Set the category

The category can be a number or a string, but in order to minimize the performance cost, it is recommended to use numbers between 0 and 7.

marker.category = 5;

Set the weight

marker.weight = 4;


marker.filtered = true|false;

Set the clustering size

You can specify a number indicating the area of the cluster. Higher number means more markers "merged". (Example)

pruneCluster.Cluster.Size = 87;

Apply the changes

Must be called when ANY changes are made.


Add custom data to marker object

Each marker has a data object where you can specify your data. = 'Roger'; = '76ez';

Setting up a Leaflet icon or a Leaflet popup

You can attach to the markers an icon object and a popup content = L.icon(...);  // See = 'Popup content';

Faster leaflet icons

If you have a lot of markers, you can create the icons and popups on the fly in order to improve their performance.

function createIcon(data, category) {
    return L.icon(...);
... = createIcon;

You can also override the PreapareLeafletMarker method. You can apply listeners to the markers here.

pruneCluster.PrepareLeafletMarker = function(leafletMarker, data) {
    leafletMarker.setIcon(/*... */); // See
    //listeners can be applied to markers in this function
    leafletMarker.on('click', function(){
    //do click event logic here
    // A popup can already be attached to the marker
    // bindPopup can override it, but it's faster to update the content instead
    if (leafletMarker.getPopup()) {
    } else {

Setting up a custom cluster icon

pruneCluster.BuildLeafletClusterIcon = function(cluster) {
    var population = cluster.population, // the number of markers inside the cluster
        stats = cluster.stats; // if you have categories on your markers
    // If you want list of markers inside the cluster
    // (you must enable the option using PruneCluster.Cluster.ENABLE_MARKERS_LIST = true)
    var markers = cluster.GetClusterMarkers() 
    return icon; // L.Icon object (See;

Listening to events on a cluster

To listen to events on the cluster, you will need to override the BuildLeafletCluster method. A click event is already specified on m, but you can add other events like mouseover, mouseout, etc. Any events that a Leaflet marker supports, the cluster also supports, since it is just a modified marker. A full list of events can be found here.

Below is an example of how to implement mouseover and mousedown for the cluster, but any events can be used in place of those.

pruneCluster.BuildLeafletCluster = function(cluster, position) {
      var m = new L.Marker(position, {
        icon: pruneCluster.BuildLeafletClusterIcon(cluster)
      m.on('click', function() {
        // Compute the  cluster bounds (it's slow : O(n))
        var markersArea = pruneCluster.Cluster.FindMarkersInArea(cluster.bounds);
        var b = pruneCluster.Cluster.ComputeBounds(markersArea);
        if (b) {
          var bounds = new L.LatLngBounds(
            new L.LatLng(b.minLat, b.maxLng),
            new L.LatLng(b.maxLat, b.minLng));
          var zoomLevelBefore = pruneCluster._map.getZoom();
          var zoomLevelAfter = pruneCluster._map.getBoundsZoom(bounds, false, new L.Point(20, 20, null));
          // If the zoom level doesn't change
          if (zoomLevelAfter === zoomLevelBefore) {
            // Send an event for the LeafletSpiderfier
  'overlappingmarkers', {
              cluster: pruneCluster,
              markers: markersArea,
              center: m.getLatLng(),
              marker: m
            pruneCluster._map.setView(position, zoomLevelAfter);
          else {
      m.on('mouseover', function() {
        //do mouseover stuff here
      m.on('mouseout', function() {
        //do mouseout stuff here
      return m;

Redraw the icons

Marker icon redrawing with a flag: = true;

Redraw all the icons:



This library was developed in context of the BRIDGE project. It is now supported by the community and we thank the contributors.


The source code of this library is licensed under the MIT License.

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