Clusterers

This document introduces the Map Clusterers , lists clusterer types, and explains how to create a clusterer and customize its settings.

The document consists of the following sections.

Overview

The Clusterer is used to aggregate map items based on their location.

This can, for example, be useful to perform density analysis.

To apply the clustering, assign one of the clusterers described below to the MapDataAdapterBase.Clusterer property.

The Marker Clusterer aggregates items using the following approach.

The center item is selected from the collection of source items.
All source items that are located closer to the item than the specified threshold along with the item form a cluster.
A cluster representative is created and added to the resulting collection. The cluster representative location is equal to the location of the center item.
All clustered items are removed from the source collection.
The previous steps are repeated until the source collection contains items.

The Marker Clusterer is represented by the MarkerClusterer class.

The Distance-based Clusterer aggregates items using the following approach.

Select an item from source items collection.
Find the closest cluster for the item.
If distance between the cluster and the item is smaller than a specified threshold, then the item is added to the cluster; otherwise, the item forms a new cluster.
The item is removed from the source collection. Update the cluster parameters. Note that the cluster representative location is the mean of cluster item locations.
The previous steps are repeated until the source collection contains items.

The Distance-based Clusterer is represented by the DistanceBasedClusterer class.

The following table represents the result comparison of clustering using the described above methods.

The clusterer	The resulting image
Marker
Distance-based

Note

To implement a custom clusterer, design a class inheriting the MapClustererBase class.

All clusterers shipped with the Map Control support items group providers and custom item factories.

Group Providers allow you to separate vector items depending on certain values. By default, the clusterers can use the predefined AttributeGroupProvider to group items by attribute values.
To customize a cluster representative, you can use the Item Settings. To do this, assign the required MapItemSettings class descendant object to the MapClusterer.ClusterSettings property.

The following examples demonstrate clusterers in action.