As an experiment, we created the Baltimore Green Week 2009 map on the OGM. It used icons to describe the topic content of events rather than to describe places, then illustrated the geographic distribution of those events. The organization Baltimore Green Works used it on their website along with a traditional Calendar of Events. Seemed successful and now is a record to refer to when planning next year's events. And we'll be able to offer it with tour routes for 2010.
http://www.opengreenmap.org/en/greenmap/baltimore-green-week-2009