This is an issue I've been trying to fix for some time too, and is especially noticeable on deployments with +10K reports or on deployments with a few thousand points but on shared hosting. The way the clustering algorithm works is that it cycles through all the available clusters or points each time to determine what to group together. As you zoom in, the number of clusters increases even if they're well outside the viewport, and the more reports there are in the system, you'll notice the system start to take major hits as it performs the clustering calculation on higher zoom levels. You can see this with my own deployment at http://crime.mapatl.com which has +30K points.

Here are some ways of fixing this issue:

Caching - Turn on caching in the admin (+v2.0). By default the system uses filecaching, so each zoom level for each category will create an individual json file. This means your system won't have to perform the clustering calculation each time. If you can use Xcache or APC caching over File caching, you'll notice better performance. Increase the cache expiration to a day if possible or 'forever' in cases where the data doesn't really change. This way the calculation will only be done once.
Restrict the calculation only to the viewport - this is written into the code but I disabled it because the calculation has to be repeated each time you pan (not just zoom) and can become quite cumbersome to the user - combined with the next point (cpu) it can be quite smooth.
More CPU!! This is the easy and expensive way out. If you have a 100K reports, you can always throw more firepower at it and perform the clustering in record time.
I'd been working on a python script which perhaps can perform the calculations faster than PHP. In my initial tests though, the performance wasn't all that much different - I'll put it up somewhere and let some python gurus figure it out. PHP functions are both its strength and weakness - in a looped calculation like this one, each function is called tens of thousands of times and that's what makes the cpu beg for mercy. Bottomline, the more points you add to the system, the greater the need for a lower level programming language - time for some HipHop PHP?

David Kobia
www.ushahidi.com
Crowdsourcing Crisis Information

Skype: dkobia

On Mon, Dec 27, 2010 at 12:23 PM, Erik Hersman <erik@...> wrote:

If anyone is online...

John McLear (@johnmclear) is having an issue where he's got a large data set and the closer he zooms in the longer and longer the points on the map take to show up, even if there aren't that many on that particular map view. Anyone have an idea what this could be and how to fix it?

He was kind enough to make a video of it:

http://www.youtube.com/watch?v=Jdj6avFH0Zg

Erik Hersman

www.ushahidi.com | www.iHub.co.ke
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