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HERE Maps API - How to cluster map markers

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[[Category:Code Examples]][[Category:Nokia Maps]][[Category:JavaScript]]
 
[[Category:Code Examples]][[Category:Nokia Maps]][[Category:JavaScript]]
{{Abstract|This article explains how to create clustered markers and reduce cluttering on the map when dealing with a very large number of markers . }}
+
{{Abstract|This article explains how to create and style clustered markers and reduce cluttering on the map when dealing with a very large number of markers . }}
 
{{ArticleMetaData <!-- v1.2 -->
 
{{ArticleMetaData <!-- v1.2 -->
 
|sourcecode= [[Media:ClusterExample.zip]]
 
|sourcecode= [[Media:ClusterExample.zip]]
Line 8: Line 8:
 
|platform= Web
 
|platform= Web
 
|devicecompatability= <!-- Compatible devices e.g.: All* (must have internal GPS) -->
 
|devicecompatability= <!-- Compatible devices e.g.: All* (must have internal GPS) -->
|dependencies= Nokia Maps 2.2.0
+
|dependencies= Nokia Maps 2.2.3
 
|signing= <!-- Signing requirements - empty or one of: Self-Signed, DevCert, Manufacturer -->
 
|signing= <!-- Signing requirements - empty or one of: Self-Signed, DevCert, Manufacturer -->
 
|capabilities= <!-- Capabilities required by the article/code example (e.g. Location, NetworkServices. -->
 
|capabilities= <!-- Capabilities required by the article/code example (e.g. Location, NetworkServices. -->
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}}
 
}}
 
{{SeeAlso|
 
{{SeeAlso|
*   [http://api.maps.nokia.com/ Nokia Maps API]  
+
* [http://developer.here.net/javascript_api Nokia Maps API]
* [http://api.maps.nokia.com/en/playground/examples/maps/map_objects/customsvgmarker.html Custom SVG graphics]
+
* [[Nokia Maps API - Short introduction to observable lists|Introduction to observable lists]]
* [http://api.maps.nokia.com/en/playground/examples/maps/heatmap/valueheatmap.html Rendering a value based heat map]
+
* [http://developer.here.net/apiexplorer/examples/api-for-js/markers/svg-marker.html Custom SVG graphics]
 +
* [http://developer.here.net/apiexplorer/examples/api-for-js/data-visualization/map-with-value-heat-map.html Rendering a value based heat map]
 
* [http://googlegeodevelopers.blogspot.fi/2009/04/markerclusterer-solution-to-too-many.html Original blog post - "A Solution to too many Markers"]
 
* [http://googlegeodevelopers.blogspot.fi/2009/04/markerclusterer-solution-to-too-many.html Original blog post - "A Solution to too many Markers"]
 +
 +
 +
* [http://developer.here.net/apiexplorer/examples/api-for-js/data-visualization/custom-cluster-theme.html Cluster Themes]
 
* [[Nokia Maps API - How to create a custom overlay|How to create a custom map overlay]]
 
* [[Nokia Maps API - How to create a custom overlay|How to create a custom map overlay]]
 +
* [http://developer.here.net/apiexplorer/examples/api-for-js/demos/overlay.html Custom overlay tile provider example]
 
  }}
 
  }}
 +
 +
{{Note |
 +
Marker clustering  has been supported within the Nokia Maps API for JavaScript itself  since version 2.2.3 of the library. See the following link for examples
 +
* [http://developer.here.net/apiexplorer/examples/api-for-js/data-visualization/custom-cluster-theme.html Cluster Themes]
 +
}}
  
 
== Introduction ==
 
== Introduction ==
When displaying a very large number of markers, it is likely that the map display will look very cluttered.  It can be difficult to understand geographical distribution of the given data set, and performance will be reduced as each marker will take time to be rendered. What is required is a method of display the data appropriately at different zooms, showing more details as the user drills down to display a smaller area. Marker '''clustering''' achieves this by summarizing the data at higher zoom levels. An illustration of the problem and its solution can be seen below.
+
When displaying a very large number of markers, it is likely that the map display will look very cluttered.  It can be difficult to understand geographical distribution of the given data set, and performance will be reduced as each marker will take time to be rendered. What is required is a method of displaying the data appropriately at different zooms, showing more details as the user drills down to display a smaller area. Marker '''clustering''' achieves this by summarizing the data at higher zoom levels. An illustration of the problem and its solution can be seen below.
  
  
Line 60: Line 70:
 
|}
 
|}
  
 +
== Standard Nokia Maps library Code Commentary ==
  
== Code Commentary ==
+
The Nokia Maps example uses the standard clustering library, and offers a simple custom theme based on SVG graphics. The key to the using custom themes is to include is to add the reference {{Icode| theme: myTheme}} when  instansitating the  {{Icode|ClusterProvider}}
The coded example provided is based upon an [http://googlegeodevelopers.blogspot.fi/2009/04/markerclusterer-solution-to-too-many.html Original Library] for the Google Maps API. Fortunately, the code is available under an [http://www.apache.org/licenses/LICENSE-2.0 Apache License], which means that it can be freely modified provided that an attribution remains. The Nokia Maps example is a derivative work which has been modified to work with the Nokia Maps API.
+
 
+
=== When to trigger the cluster function  ===
+
The code works by making a re-calculation whenever the view port is moved, or the zoom level changed, this can be achieved by adding in a {{Icode|eventListener}} to the  '''mapviewchangeend''' {{Icode| Event}} and an {{Icode|observer}} to the '''zoomLevel''' property,
+
  
 
<code javascript>
 
<code javascript>
var eventHandler = function (evt) {    
+
var ClusterProvider = nokia.maps.clustering.ClusterProvider,
      me_.resetViewport();
+
clusterProvider = new ClusterProvider(display, {
};
+
eps: 16,
 +
minPts: 1,
 +
dataPoints: [],
 +
theme : myTheme
 +
});
  
  map_.addListener("mapviewchangeend", eventHandler);  
+
// Data Points in the form off latitude, longitiude
  map_.addObserver("zoomLevel", eventHandler);
+
....
 +
clusterProvider.addAll(dataPoints);
 +
clusterProvider.cluster();
 
</code>
 
</code>
  
When the view port is changed, the array of all {{Icode|markers}} is distributed into two buckets, those withing the current view port and those left outside - Only those which remain on screen are processed further. Each {{Icode|marker}} left on screen is tested to see if it is close to any {{Icode|markers}} processed previously. If so it is added to that cluster, otherwise it is added to its own cluster. Essentially the flow of this code is unchanged form the original example. If a cluster has more than one marker, the cluster is rendered using [http://api.maps.nokia.com/en/playground/examples/maps/map_objects/customsvgmarker.html SVG graphics]
+
{{Icode|myTheme}} itself holds two functions:
  
 
<code javascript>
 
<code javascript>
var markerIcon = createIcon(this.getTotalMarkers());
+
// Set up a theme.
clusterMarker_ = new nokia.maps.map.Marker(center_ ,  
+
var myTheme ={
{icon: markerIcon}
+
  getClusterPresentation :  getClusterPresentation ,
);
+
  getNoisePresentation : getNoisePresentation
map_.objects.add (  clusterMarker_);
+
};
 
</code>
 
</code>
 +
 +
Where the {{Icode|getClusterPresentation()}} and getNoisePresentation - the functions style the data from the cluster. The former is displayed using SVG Graphics (see below), and the latter using a {{Icode|StandardMarker}}
 +
 +
<code javascript>
 +
// This is called for a cluster of points...
 +
var getClusterPresentation = function (dataPoints) {
 +
 +
if (dataPoints.getSize() > 0){
 +
return new nokia.maps.map.StandardMarker (dataPoints.getBounds().getCenter(),
 +
 +
text:  dataPoints.getSize(), 
 +
brush: {color: '#FF0000'}           
 +
}
 +
);
 +
}
 +
};
 +
 +
 +
// This is called for an individual point which is outside of a cluster.
 +
var getNoisePresentation = function (dataPoint) {
 +
return new nokia.maps.map.StandardMarker ([dataPoint.latitude, dataPoint.longitude]);
 +
};
 +
</code>
 +
 +
 +
 +
=== Using SVG Graphic Markers ===
  
 
The SVG graphic consists of three concentric circles with the marker count within it.
 
The SVG graphic consists of three concentric circles with the marker count within it.
Line 128: Line 168:
  
  
 +
 +
 +
== Alternative Google library Code Commentary ==
 +
The coded example provided  also offers a version based upon an [http://googlegeodevelopers.blogspot.fi/2009/04/markerclusterer-solution-to-too-many.html Original Library] for the Google Maps API. Fortunately, the code is available under an [http://www.apache.org/licenses/LICENSE-2.0 Apache License], which means that it can be freely modified provided that an attribution remains. The Nokia Maps example is a derivative work which has been modified to work with the Nokia Maps API.
 +
 +
=== When to trigger the cluster function  ===
 +
The code works by making a re-calculation whenever the view port is moved, or the zoom level changed, this can be achieved by adding in an {{Icode|eventListener}} to the  '''mapviewchangeend''' {{Icode| Event}} and an {{Icode|observer}} to the '''zoomLevel''' property,
 +
 +
<code javascript>
 +
var eventHandler = function (evt) {   
 +
      me_.resetViewport();
 +
};
 +
 +
  map_.addListener("mapviewchangeend", eventHandler);
 +
  map_.addObserver("zoomLevel", eventHandler);
 +
</code>
 +
 +
When the view port is changed, the array of all {{Icode|markers}} is distributed into two buckets, those withing the current view port and those left outside - Only those which remain on screen are processed further. Each {{Icode|marker}} left on screen is tested to see if it is close to any {{Icode|markers}} processed previously. If so it is added to that cluster, otherwise it is added to its own cluster. Essentially the flow of this code is unchanged form the original example. If a cluster has more than one marker, the cluster is rendered using [http://api.maps.nokia.com/en/playground/examples/maps/map_objects/customsvgmarker.html SVG graphics]
 +
 +
<code javascript>
 +
var markerIcon = createIcon(this.getTotalMarkers());
 +
clusterMarker_ = new nokia.maps.map.Marker(center_ ,
 +
{icon: markerIcon}
 +
);
 +
map_.objects.add (  clusterMarker_);
 +
</code>
 
=== Adding an OList wrapper ===
 
=== Adding an OList wrapper ===
 
The code for the addition/removal of the markers for clustering is held in the {{Icode|addMarkers()}},  {{Icode|addMarker()}},  {{Icode|clearMarkers()}},  {{Icode| removeMarker()}} methods, these are taken from the original library, and have only been converted as necessary. To update these methods to use the familiar {{Icode|nokia.maps.util.OList()}} interface for adding/removing {{Icode|markers}}, the original methods have been wrapped as shown:
 
The code for the addition/removal of the markers for clustering is held in the {{Icode|addMarkers()}},  {{Icode|addMarker()}},  {{Icode|clearMarkers()}},  {{Icode| removeMarker()}} methods, these are taken from the original library, and have only been converted as necessary. To update these methods to use the familiar {{Icode|nokia.maps.util.OList()}} interface for adding/removing {{Icode|markers}}, the original methods have been wrapped as shown:
Line 167: Line 233:
 
</code>
 
</code>
  
== How to use the marker clusterer library  ==
+
=== How to use the alternative marker clusterer library  ===
 
The {{Icode|MarkerClusterer}}  library is available as a separate JavaScript file. To use it, include a link to the file in the {{Icode|&lt;header&gt;}} of your page.
 
The {{Icode|MarkerClusterer}}  library is available as a separate JavaScript file. To use it, include a link to the file in the {{Icode|&lt;header&gt;}} of your page.
 
<code javascript>
 
<code javascript>
Line 199: Line 265:
 
* {{Icode|clusterer.objects.remove(marker);}} to remove a single marker from the  {{Icode|MarkerClusterer}}
 
* {{Icode|clusterer.objects.remove(marker);}} to remove a single marker from the  {{Icode|MarkerClusterer}}
 
* {{Icode|clusterer.objects.removeAll(markers);}} to remove an {{Icode|Array}} of markers from the  {{Icode|MarkerClusterer}}
 
* {{Icode|clusterer.objects.removeAll(markers);}} to remove an {{Icode|Array}} of markers from the  {{Icode|MarkerClusterer}}
* {{Icode|clusterer.objects.removeAt(index);}} to remove a specified markerat the given index from the  {{Icode|MarkerClusterer}}
+
* {{Icode|clusterer.objects.removeAt(index);}} to remove a specified marker at the given index from the  {{Icode|MarkerClusterer}}
  
  
  
 
== Summary ==
 
== Summary ==
The [[Media:ClusterExample.zip|Code Example]]  adds 7000 random markers to a map and demonstrates the use of the {{Icode|MarkerClusterer}} on a Nokia Map. This is a '''client''' side library which works reasonably well for a large number of markers,  but performance is reduced when the number of markers reaches the tens of thousands,  where it starts to trigger "slow Script" dialogs in Internet Explorer for example. 'The performance of  '''client''' side libraries is inextricably linked to the performance of the web browser used. For even larger numbers of markers the only solution would be to trigger the calculations '''server''' side instead, to introduce view port based {{Icode|marker}} management or to introduce a [[Nokia Maps API - How to create a custom overlay|map overlay]]
+
The [[Media:ClusterExample.zip|Code Example]]  adds 7000 random markers to a map and demonstrates the use of both the standard clustering library and the alternative the {{Icode|MarkerClusterer}} component on a Nokia Map. This is a '''client''' side library which works reasonably well for a large number of markers,  but performance is reduced when the number of markers reaches the tens of thousands,  where it starts to trigger "slow Script" dialogs in Internet Explorer for example. 'The performance of  '''client''' side libraries is inextricably linked to the performance of the web browser used. For even larger numbers of markers the only solution would be to trigger the calculations '''server''' side instead, to introduce view port based {{Icode|marker}} management or to introduce a [[Nokia Maps API - How to create a custom overlay|map overlay]]

Revision as of 18:30, 3 January 2013

This article explains how to create and style clustered markers and reduce cluttering on the map when dealing with a very large number of markers .

Article Metadata
Code ExampleTested with
Devices(s): Internet Explorer, Google Chrome, Firefox
Compatibility
Platform(s): Web
Dependencies: Nokia Maps 2.2.3
Article
Keywords: Nokia Maps, Marker, Cluster, Large Dataset
Created: jasfox (12 Jun 2012)
Last edited: jasfox (03 Jan 2013)

Note.pngNote: Marker clustering has been supported within the Nokia Maps API for JavaScript itself since version 2.2.3 of the library. See the following link for examples

Contents

Introduction

When displaying a very large number of markers, it is likely that the map display will look very cluttered. It can be difficult to understand geographical distribution of the given data set, and performance will be reduced as each marker will take time to be rendered. What is required is a method of displaying the data appropriately at different zooms, showing more details as the user drills down to display a smaller area. Marker clustering achieves this by summarizing the data at higher zoom levels. An illustration of the problem and its solution can be seen below.


UnClusteredMap.png
Map at low zoom displaying 2000 Markers distributed between

Texas and the Eastern Seaboard of the U.S.A.


ClusterMap1.png
Cluster Map at low zoom summarizing 2000 Markers distributed between

Texas and the Eastern Seaboard of the U.S.A.


ClusterMap2.png
Cluster map at a higher zoom, showing the Eastern Seaboard only

Standard Nokia Maps library Code Commentary

The Nokia Maps example uses the standard clustering library, and offers a simple custom theme based on SVG graphics. The key to the using custom themes is to include is to add the reference theme: myTheme when instansitating the ClusterProvider

var ClusterProvider = nokia.maps.clustering.ClusterProvider,
clusterProvider = new ClusterProvider(display, {
eps: 16,
minPts: 1,
dataPoints: [],
theme : myTheme
});
 
// Data Points in the form off latitude, longitiude
....
clusterProvider.addAll(dataPoints);
clusterProvider.cluster();

myTheme itself holds two functions:

// Set up a theme.
var myTheme ={
getClusterPresentation : getClusterPresentation ,
getNoisePresentation : getNoisePresentation
};

Where the getClusterPresentation() and getNoisePresentation - the functions style the data from the cluster. The former is displayed using SVG Graphics (see below), and the latter using a StandardMarker

// This is called for a cluster of points...
var getClusterPresentation = function (dataPoints) {
 
if (dataPoints.getSize() > 0){
return new nokia.maps.map.StandardMarker (dataPoints.getBounds().getCenter(),
{
text: dataPoints.getSize(),
brush: {color: '#FF0000'}
}
);
}
};
 
 
// This is called for an individual point which is outside of a cluster.
var getNoisePresentation = function (dataPoint) {
return new nokia.maps.map.StandardMarker ([dataPoint.latitude, dataPoint.longitude]);
};


Using SVG Graphic Markers

The SVG graphic consists of three concentric circles with the marker count within it.

'<svg width="39" height="39" xmlns="http://www.w3.org/2000/svg">' +
'<circle stroke="#FFF" fill="__MAINCOLOR__" cx="19" cy="19" r="19" stroke-width="2" />' +
'<circle stroke="#FFF" fill="__MAINCOLOR__" cx="19" cy="19" r="15" stroke-width="2"/>' +
'<circle stroke="#FFF" fill="__MAINCOLOR__" cx="19" cy="19" r="11" stroke-width="2"/>' +
'<text x="19" y="23" font-size="10pt" font-family="arial" font-weight="bold" text-anchor="middle" fill="#FFF" textContent="__TEXTCONTENT__">__TEXT__</text>' +
'</svg>

The color and marker count placeholders are filled in when the image is returned:

var stops = {
"0": "#8A8A8A", //Grey for 0-10
"10": "#CACA00", //Yellow for 11-50
"50": "#00CC00", //Green for 51-100
"100": "#0000CC", //Blue for 101-200
"200": "#CC00CC", //Purple for 201-500
"500": "#FF0000" //Red for over 500
};
var svgParser = new nokia.maps.gfx.SvgParser();
 
createIcon = function (count, mainColor) {
 
[...]
for (var i in stops) {
if (count > i){
color = stops[i];
}
}
 
var svg = iconSVG[digit]
.replace(/__TEXTCONTENT__/g, count)
.replace(/__TEXT__/g, count)
.replace(/__MAINCOLOR__/g, color);
return new nokia.maps.gfx.GraphicsImage(svgParser.parseSvg(svg));
};



Alternative Google library Code Commentary

The coded example provided also offers a version based upon an Original Library for the Google Maps API. Fortunately, the code is available under an Apache License, which means that it can be freely modified provided that an attribution remains. The Nokia Maps example is a derivative work which has been modified to work with the Nokia Maps API.

When to trigger the cluster function

The code works by making a re-calculation whenever the view port is moved, or the zoom level changed, this can be achieved by adding in an eventListener to the mapviewchangeend Event and an observer to the zoomLevel property,

 var eventHandler = function (evt) {     
me_.resetViewport();
};
 
map_.addListener("mapviewchangeend", eventHandler);
map_.addObserver("zoomLevel", eventHandler);

When the view port is changed, the array of all markers is distributed into two buckets, those withing the current view port and those left outside - Only those which remain on screen are processed further. Each marker left on screen is tested to see if it is close to any markers processed previously. If so it is added to that cluster, otherwise it is added to its own cluster. Essentially the flow of this code is unchanged form the original example. If a cluster has more than one marker, the cluster is rendered using SVG graphics

var markerIcon = createIcon(this.getTotalMarkers());
clusterMarker_ = new nokia.maps.map.Marker(center_ ,
{icon: markerIcon}
);
map_.objects.add ( clusterMarker_);

Adding an OList wrapper

The code for the addition/removal of the markers for clustering is held in the addMarkers(), addMarker(), clearMarkers(), removeMarker() methods, these are taken from the original library, and have only been converted as necessary. To update these methods to use the familiar nokia.maps.util.OList() interface for adding/removing markers, the original methods have been wrapped as shown:

function MarkerClusterer(map, opt_markers) {
...
ExtendedOList.prototype = new nokia.maps.util.OList();
function ExtendedOList (){
this.addAll = function (elements){
ExtendedOList.prototype.addAll.call(this, elements);
addMarkers(elements);
}
this.add = function (element){
ExtendedOList.prototype.add.call(this, element);
addMarker(element);
}
this.clear= function (){
clearMarkers();
ExtendedOList.prototype.clear.call(this);
}
this.remove= function (element){
removeMarker(element)
ExtendedOList.prototype.remove.call(this);
}
this.removeAt= function (idx){
removeMarker( ExtendedOList.prototype.get.call(this,idx));
ExtendedOList.prototype.removeAt.call(this,idx);
}
 
this.removeAll= function (elements){
for (var i = 0; i < elements.length; ++i) {
removeMarker( elements[i]);
}
ExtendedOList.prototype.removeAll.call(this,elements);
}
}
this.objects = new ExtendedOList();
etc...

How to use the alternative marker clusterer library

The MarkerClusterer library is available as a separate JavaScript file. To use it, include a link to the file in the <header> of your page.

<script type="text/javascript" charset="UTF-8" src="./markerclusterer.js"></script>

To cluster the markers place them into an array, and create the MarkerClusterer as shown, and and call MarkerClusterer.objects.addAll()

var markers = [];
for (var i = 0; i < size; i++){
var marker = new nokia.maps.map.StandardMarker (randomPointNear (lat, long, spread) );
markers.push(marker);
}
 
var markerCluster = new MarkerClusterer();
markerCluster.objects.addAll(markers);

The MarkerClusterer class has been written as a nokia.maps.map.component.Component . To display the clustered markers on a map, attach the component to the MapDisplay.

display.addComponent(markerCluster);

The MarkerClusterer exposes a single objects property for manipulating the markers. As expected this ordered list of objects exposes an nokia.maps.util.OList interface, and markers can be added, removed and queried in the same familar manner as objects in a nokia.maps.map.Container

  • clusterer.objects.add(marker); to add a single marker to the MarkerClusterer
  • clusterer.objects.addAll(markers); to add an Array of markers
  • clusterer.objects.clear(); to empty all markers from the MarkerClusterer
  • clusterer.objects.getLength(); to find the total number of markers clustered.
  • clusterer.objects.remove(marker); to remove a single marker from the MarkerClusterer
  • clusterer.objects.removeAll(markers); to remove an Array of markers from the MarkerClusterer
  • clusterer.objects.removeAt(index); to remove a specified marker at the given index from the MarkerClusterer


Summary

The Code Example adds 7000 random markers to a map and demonstrates the use of both the standard clustering library and the alternative the MarkerClusterer component on a Nokia Map. This is a client side library which works reasonably well for a large number of markers, but performance is reduced when the number of markers reaches the tens of thousands, where it starts to trigger "slow Script" dialogs in Internet Explorer for example. 'The performance of client side libraries is inextricably linked to the performance of the web browser used. For even larger numbers of markers the only solution would be to trigger the calculations server side instead, to introduce view port based marker management or to introduce a map overlay

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