Deals with overlapping markers in Google Maps JS API v3, Google Earth-style
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Overlapping Marker Spiderfier for Google Maps API v3

Ever noticed how, in Google Earth, marker pins that overlap each other spring apart gracefully when you click them, so you can pick the one you wanted?

Ever noticed how, when using the Google Maps API, the same thing doesn’t happen?

This library makes map markers in the Google Maps API (version 3) behave in that Google Earth way (minus the animation). Small numbers of markers (yes, up to 8) spiderfy into a circle. Larger numbers fan out into a more space-efficient spiral.

The compiled code has no dependencies beyond Google Maps. Compiled out of CoffeeScript, minified with Google’s Closure Compiler and gzipped, it’s under 4KB.

I originally wrote it as part of Mappiness. There is also a port for the Leaflet maps API, which has fewer features.

Doesn’t clustering solve this problem?

You may have seen the marker clustering library, which also helps deal with markers that are close together.

That might be what you want. However, it probably isn’t what you want (or isn’t the only thing you want) if you have markers that could be in the exact same location, or close enough to overlap even at maximum zoom. In that case, clustering won’t help your users see and/or click on the marker they’re looking for.

(I’m told that the OverlappingMarkerSpiderfier plays nice with clustering — i.e. once you get down to a zoom level where individual markers are shown, these markers then spiderfy happily — but I haven’t yet tried it myself).

What’s new?

1.0

Version 1.0 brings three key enhancements:

  • Easy differential formatting of markers that will and won’t spiderfy on click (via a new event listener). Thanks go to Graphileon for sponsoring this much-requested feature.
  • Simplified integration, via a per-marker spider_click listener that’s a direct replacement for the standard click listener.
  • Support for async/deferred loading in parallel with Google Maps. We no longer require the Google Maps API to be loaded first.

Also, a few potentially breaking changes:

  • The methods addMarker(), removeMarker() and clearMarkers() have been renamed to trackMarker(), forgetMarker() and forgetAllMarkers(). This better reflects what they do. At the same time, new shortcut methods addMarker(), removeMarker() and removeAllMarkers() have been added — these call trackMarker(), forgetMarker() or forgetAllMarkers() respectively and also add or remove the relevant marker(s) from the Google Map itself.

If you’ve only been using addMarker() and removeMarker(), and you always add or remove your markers from the map at the same time as the spiderfier, you won’t need to do anything new.

0.3

Breaking changes:

  • The willSpiderfy(marker) and markersThatWillAndWontSpiderfy() methods were replaced by the (similar, but different) markersNearMarker(marker) and markersNearAnyOtherMarker() methods. This should only worry advanced users.

Demo

There are three demo maps, showing increasing levels of functionality and complexity. Studying the source of these may well be the best way to understand how to use this library.

In all cases, the data is randomised: reload the map to reposition the markers.

Download

Download the compiled, minified JS source.

How to use

See the source of the demo maps, or follow along here for a slightly simpler usage with commentary.

Simplest integration

Create a map and an InfoWindow as per usual:

var mapElement = document.getElementById('map_element');
var map = new google.maps.Map(mapElement, { center: new google.maps.LatLng(50, 0), zoom: 6 });
var iw = new google.maps.InfoWindow();

Now create an OverlappingMarkerSpiderfier instance associated with the map (the three options set here are not required, but will save some memory and CPU in simple use cases like this one):

var oms = new OverlappingMarkerSpiderfier(map, { 
  markersWontMove: true, 
  markersWontHide: true,
  basicFormatEvents: true
});

As you create your markers, instead of attaching click listeners, attach spider_click listeners.

And, instead of adding them to the map with marker.setMap(map), add them to your OverlappingMarkerSpiderfier instance (and the map too) with oms.addMarker(marker).

for (var i = 0, len = window.mapData.length; i < len; i ++) {
  (function() {  // make a closure over the marker and marker data
    var markerData = window.mapData[i];  // e.g. { lat: 50.123, lng: 0.123, text: 'XYZ' }
    var marker = new google.maps.Marker({ position: markerData });  // markerData works here as a LatLngLiteral
    google.maps.event.addListener(marker, 'spider_click', function(e) {  // 'spider_click', not plain 'click'
      iw.setContent(markerData.text);
      iw.open(map, marker);
    });
    oms.addMarker(marker);  // adds the marker to the spiderfier _and_ the map
  })();
}

Marker formatting

New in version 1.0, you can add marker formatting listeners to differentiate between markers that will and won’t spiderfy (and that are and aren’t spiderfied).

You can either add a format listener to the spiderfier instance (simplest if all your markers look the same, aside from their spiderfying status), or a spider_format listener to each individual marker (useful if you independently have different marker styles).

The first of these options, as seen in the standard demo source, looks something like this:

oms.addListener('format', function(marker, status) {
  var iconURL = status == OverlappingMarkerSpiderfier.markerStatus.SPIDERFIED ? 'marker-highlight.svg' :
    status == OverlappingMarkerSpiderfier.markerStatus.SPIDERFIABLE ? 'marker-plus.svg' :
    status == OverlappingMarkerSpiderfier.markerStatus.UNSPIDERFIABLE ? 'marker.svg' : 
    null;
  marker.setIcon({
    url: iconURL,
    scaledSize: new google.maps.Size(23, 32);  // makes SVG icons work in IE
  });
});

For an example of the second, per-marker option, see the fancy demo source.

Again, thanks to Graphileon for sponsoring this feature.

Docs

Loading

The Google Maps API code changes frequently. Some earlier versions had broken support for z-indices, and the ‘frozen’ versions appear not to be as frozen as you’d like. At this moment, the ‘stable’ version 3.27 seems to work well, but do test with whatever version you fix on. Sometimes, glitches can be fixed by setting the optimized: false on your markers.

To enable async/deferred loading, as used by the Google Maps library itself, you can either provide a top-level function named spiderfier_callback, or specify a spiderfier_callback parameter that names some other top-level function in the script src attribute (i.e. <script src="/path/to/oms.min.js?spiderfier_callback=myCallbackFunction"><script>).

Construction

new OverlappingMarkerSpiderfier(map, options)

Creates an instance associated with map (a google.maps.Map).

The options argument is an optional Object specifying any options you want changed from their defaults. The available options are:

markersWontMove (default: false)
markersWontHide (default: false)

By default, change events for each added marker’s position and visibility are observed (so that, if a spiderfied marker is moved or hidden, all spiderfied markers are unspiderfied, and the new position is respected where applicable).

However, if you know that you won’t be moving and/or hiding any of the markers you add to this instance, you can save memory (a closure per marker in each case) by setting the options named markersWontMove and/or markersWontHide to true.

For example, var oms = new OverlappingMarkerSpiderfier(map, {markersWontMove: true, markersWontHide: true});.

basicFormatEvents (default: false)

By default, marker status is recalculated for all markers on any relevant change, triggering any 'spider_format' marker listeners and 'format' instance listeners, with one of the following status values:

OverlappingMarkerSpiderfier.markerStatus.SPIDERFIED
OverlappingMarkerSpiderfier.markerStatus.SPIDERFIABLE
OverlappingMarkerSpiderfier.markerStatus.UNSPIDERFIABLE

This recalculation can be quite CPU intensive for large numbers of markers, so if you don’t intend to format markers differently depending on whether they will spiderfy when clicked, you should opt out of this behaviour by setting basicFormatEvents to true.

Then the 'spider_format' and 'format' listeners will receive only these status values instead:

OverlappingMarkerSpiderfier.markerStatus.SPIDERFIED
OverlappingMarkerSpiderfier.markerStatus.UNSPIDERFIED

keepSpiderfied (default: false)

By default, the OverlappingMarkerSpiderfier works like Google Earth, in that when you click a spiderfied marker, the markers unspiderfy before any other action takes place.

Since this can make it tricky for the user to work through a set of markers one by one, you can override this behaviour by setting the keepSpiderfied option to true. Note that the markers will still be unspiderfied if any other marker than those in the currently spiderfied set are clicked.

ignoreMapClick (default: false)

By default, clicking an empty spot on the map causes spiderfied markers to unspiderfy. Setting this option to true suppresses that behaviour.

nearbyDistance (default: 20).

This is the pixel radius within which a marker is considered to be overlapping a clicked marker.

circleSpiralSwitchover (default: 9)

This is the lowest number of markers that will be fanned out into a spiral instead of a circle. Set this to 0 to always get spirals, or Infinity for all circles.

legWeight (default: 1.5)

This determines the thickness of the lines joining spiderfied markers to their original locations.

Instance methods: managing markers

Note: methods that have no obvious return value return the OverlappingMarkerSpiderfier instance they were called on, in case you want to chain method calls.

trackMarker(marker, listener)

Starts tracking marker (a google.maps.Marker), but does not add it to the map. If listener is specified, it is attached to the marker as a spider_click listener.

addMarker(marker, listener)

Starts tracking marker (a google.maps.Marker) and adds it to the map. If listener is specified, it is attached to the marker as a spider_click listener.

forgetMarker(marker)

Stops marker being tracked, but does not remove it from the map (to remove a marker from the map you must call setMap(null) on it, as per usual, or call removeMarker(marker) instead).

removeMarker(marker)

Stops marker being tracked and removes it from the map.

forgetAllMarkers()

Stops every marker being tracked. Much quicker than calling forgetMarker(marker) in a loop, since that has to search the markers array every time.

This does not remove the markers from the map (to remove the markers from the map you must call setMap(null) on each of them, as per usual, or call removeAllMarkers() instead).

removeAllMarkers()

Stops every marker being tracked, and removes them all from the map. Much quicker than calling removeMarker(marker) in a loop, since that has to search the markers array every time.

getMarkers()

Returns an array of all the markers that are currently being tracked. This is a copy of the one used internally, so you can do what you like with it.

Marker events

New from version 1.0, two new events are supported on your markers.

'spider_click'

The 'spider_click' event is triggered on a marker when it (a) has no markers nearby and is clicked, or (b) has been spiderfied along with nearby markers, and is then clicked. In general, you’ll want to replace your 'click' listeners with 'spider_click' listeners when integrating the OverlappingMarkerSpiderfier library.

'spider_format'

The 'spider_format' event is triggered when the spiderfying status of a marker could have changed. That could be because this marker began to be tracked, because other markers were added, removed or hidden, or because the zoom level changed.

You can use a listener on this event to make a visual distinction between markers that are a) unspiderfied and will not spiderfy when clicked, b) unspiderfied and will spiderfy when clicked, or c) spiderfied.

The listener function receives one argument, which is a status value (one of OverlappingMarkerSpiderfier.markerStatus.SPIDERFIED, OverlappingMarkerSpiderfier.markerStatus.SPIDERFIABLE or OverlappingMarkerSpiderfier.markerStatus.UNSPIDERFIABLE for standard formatting events; or one of OverlappingMarkerSpiderfier.markerStatus.SPIDERFIED or OverlappingMarkerSpiderfier.markerStatus.UNSPIDERFIED if formatting events have been restricted, for efficiency, via the basicFormatEvents option).

Instance methods: managing listeners

addListener(event, listenerFunc)

Adds a listener to react to one of four events.

event may be 'click', 'format', 'spiderfy' or 'unspiderfy'.

For 'click' events, listenerFunc receives one argument: the clicked marker object. You’ll probably want to use this listener to do something like show a google.maps.InfoWindow. Note that this is the traditional method of responding to a marker click, but you may well now find it easier to add a separate 'spider_click' event to each marker instead.

For 'format' events, listenerFunc receives two arguments: a marker object, and a status value (one of OverlappingMarkerSpiderfier.markerStatus.SPIDERFIED, OverlappingMarkerSpiderfier.markerStatus.SPIDERFIABLE or OverlappingMarkerSpiderfier.markerStatus.UNSPIDERFIABLE for standard formatting events; or one of OverlappingMarkerSpiderfier.markerStatus.SPIDERFIED or OverlappingMarkerSpiderfier.markerStatus.UNSPIDERFIED if only basic formatting events have been requested, for efficiency, via the basicFormatEvents option).

For 'spiderfy' or 'unspiderfy' events, listenerFunc receives two arguments: first, an array of the markers that were spiderfied or unspiderfied; second, an array of the markers that were not. Traditionally, one use for these listeners was to make some distinction between spiderfied and non-spiderfied markers when some markers are spiderfied — e.g. highlighting those that are spiderfied, or dimming out those that aren’t. However, the newer 'format' event is now a better and more flexible way to do this.

removeListener(event, listenerFunc)

Removes the specified listener on the specified event.

clearListeners(event)

Removes all listeners on the specified event.

unspiderfy()

Returns any spiderfied markers to their original positions, and triggers any listeners you may have set for this event. Unless no markers are spiderfied, in which case it does nothing.

Instance methods: advanced use only!

These methods were previously provided mainly to enable differential marker formatting according to whether a marker would spiderfy when clicked; since this is now supported explicitly, you’re quite unlikely to need them.

markersNearMarker(marker, firstOnly)

Returns an array of markers within nearbyDistance pixels of marker — i.e. those that will be spiderfied when marker is clicked. If you pass true as the second argument, the search will stop when a single marker has been found. This is more efficient if all you want to know is whether there are any nearby markers.

Don’t call this method in a loop over all your markers, since this can take a very long time.

The return value of this method may change any time the zoom level changes, and when any marker is added, moved, hidden or removed. Hence you’ll very likely want call it (and take appropriate action) every time the map’s zoom_changed event fires and any time you add, move, hide or remove a marker.

Note also that this method relies on the map’s Projection object being available, and thus cannot be called until the map’s first idle event fires.

markersNearAnyOtherMarker()

Returns an array of all markers that are near one or more other markers — i.e. those will be spiderfied when clicked.

This method is several orders of magnitude faster than looping over all markers calling markersNearMarker (primarily because it only does the expensive business of converting lat/lons to pixel coordinates once per marker).

The return value of this method may change any time the zoom level changes, and when any marker is added, moved, hidden or removed. Hence you’ll very likely want call it (and take appropriate action) every time the map’s zoom_changed event fires and any time you add, move, hide or remove a marker.

Note also that this method relies on the map’s Projection object being available, and thus cannot be called until the map’s first idle event fires.

Properties

You can set the following properties on an OverlappingMarkerSpiderfier instance:

legColors.usual[mapType] and legColors.highlighted[mapType]

These determine the usual and highlighted colours of the lines, where mapType is one of the google.maps.MapTypeId constants (or a custom map type ID).

The defaults are as follows:

var mti = google.maps.MapTypeId;
legColors.usual[mti.HYBRID] = legColors.usual[mti.SATELLITE] = '#fff';
legColors.usual[mti.TERRAIN] = legColors.usual[mti.ROADMAP] = '#444';
legColors.highlighted[mti.HYBRID] = legColors.highlighted[mti.SATELLITE] = 
  legColors.highlighted[mti.TERRAIN] = legColors.highlighted[mti.ROADMAP] = '#f00';

You can also get and set any of the options noted in the constructor function documentation above as properties on an OverlappingMarkerSpiderfier instance. However, for some of these options (e.g. markersWontMove) modifications won’t be applied retroactively.

Licence

This software is released under the MIT licence.

Finally, if you want to say thanks, I am on Gittip.