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Some Visual and Interaction Options for Clustering

When it comes to clustering point layers on a map, there are two main aesthetic questions to consider (questions we are used to asking of just about anything):

How does it look?
How does it act?


The Generic Cluster

The Generic Cluster method should be used when different point layers are clustering together, as some kind of melting pot cluster.  Think, Everybody Get Together, by the Dave Clark Five.  The Generic Cluster icon should be a relatively basic graphic that does not correlate too closely to the icon of any specific data layer being clustered, but is rather a visual indication that says, "more data here" with some graphical invitation to zoom in or get more.

The Scaled Original Cluster

The Scaled Original cluster method should be used when the application is set to cluster only within like-layers.  It is a larger version of the icon that is used for that individual layer.  For example, vessels represented by blue dots would have a cluster icon that looked like a bigger blue dot.  If multiple map layers have clustering turned on individually, then each layer’s cluster icon is simply a scaled-up version.  In the image above, the two layers have clustering turned on; I can see where clusters for individual vessel types because I see blue clusters and red clusters.

These scaled icons could be simply larger (yes, this is a cluster) or the largeness could correspond to the quantity of children it represents.  The latter would be more technically involved.

Don’t use the Scaled Original method if icons are already being thematically scaled to represent a data value.  It is important to isolate the visual variable of icons, and if size already means something then don’t hijack that visual variable for clustering as well.

The Quantity Label

The Quantity Label method places a number over each of the cluster icons.  This method can be used in tandem with the generic dedicated cluster icon or the Layer-Specific method, but care must be used when implementing an automated number label, as the level of complexity of the icon can be obscured by the label -leading to unreadable results.


So I have a visual indication on the map of a cluster.  What about when I hover over it or click it?  Here are some options…

    • On Rollover
      • A radial tethered blowout of component child icons
      • A hyperlink list of composite children
      • A tooltip message denoting the number of children
    • On Click
      • Alternatively, any of the above
      • Zoom in one increment, centered on clicked cluster
      • Zoom to extents of clustered children
      • Zoom in on the location of the clicked hyperlink or tethered icon

John Nelson / IDV Solutions / john.nelson@idvsolutions.com


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