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    <p>If the requirement is to cluster a fairly small number of points, perhaps less than 1000, then Solr needn't be involved. Grab the points and plot them using something like <a href="http://www.patrick-wied.at/static/heatmapjs/">HeatmapJS</a>.</p> <p>I presume the requirement is to cluster <em>all</em> results in a search which may potentially be many thousands or even millions of documents. I suggest starting with generating a heatmap of the densities over a grid of the search area. You can do this by indexing each point encoded in geohash form at each length (e.g. D2RY, D2R, D2, D). But then precede the length by how long it is: 4_D2RY, 3_D2R, 2_D2, 1_D. These little strings go into a multi-valued "string" type field in Solr that you will then facet on. When faceting, you'll come up with a suitable grid resolution (e.g. goehash prefix length) and then use that as a prefix query, like facet.prefix=4_ You can index the point using a LatLonType field separately and do a standard bounding box query there. At this point, you're faceted search results will give you the information to fill in a grid of numbers. The beauty of this scheme is that it is <em>fast</em> -- you could generate such heat-maps on the fly. It will use a fair amount of RAM though since this is faceting on a multi-valued field that will have a ton of values. This is something I want to add to the new Lucene spatial module (or perhaps at the Solr layer) in a way that won't need extra memory and to make it easy. It won't make it to Solr 4.0, but maybe 4.1.</p> <p>At this stage, perhaps a heatmap is fine as-is. But you may want to apply clustering on top of this, as your question states. Someone tipped me off to some <a href="http://web.archive.org/web/20071121140547/http://trib.tv/tech/clustering-points-on-a-google-map/">interesting geo clustering algorithms</a> that can be applied to heatmaps.</p>
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    1. POGeoclusters in SOLR
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    1. USDavid Smiley
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    1. COAny update on whether this is going to make it into 4.1?
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      1. USbikedorkseattle
    2. CONope. Long ago I would have bet money on it being a priority but it just hasn't been.
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      1. USDavid Smiley
    3. COThis is a really neat solution. Did you come up with that solution yourself? I had to read it about 5 times before I understood how it works...
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