Interesting stats about types of weapons, locations, whether weapon was acquired legally, and gender of killer, etc. Would be nice to see trends on a chart.
Read full article (where you will be able to zoom in on the map) at http://www.motherjones.com/politics/2012/07/mass-shootings-map. See also the 2nd page for details about shootings, displayed in a timeline. The one that occurred this week in DC is not yet listed.