Heatmaps provide a clear visual display of densities of features for easier analysis:

 * [http://boston.povo.com/Beacon_Hill?heatmap&radius=GreaterBoston&tags=atm ATMs in Beacon Hill, Boston]
 * [http://blog.corunet.com/the-definitive-heatmap/ Clickmaps]
 * [http://code.google.com/p/gheat/ gHeat] - heatmaps for Google Maps
 * [http://dev.openlayers.org/sandbox/vector-behavior/examples/strategy-cluster.html OpenLayers' Cluster Strategy] (which we already use)

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[wiki:BluePrintGeographicInformationSystems GIS BluePrints]