The yellow circle is San Bernardino, sized to initial, unconfirmed reports of the victims so far. (The San Bernardino Fire Department has said there are believed to be at least 20 people injured in the shooting.) The blue circles are those in which people were killed; outlined circles are the number injured.
There have been incidents that meet the ShootingTracker standard in 46 states and in D.C. Florida, Illinois and California have had the most incidents. In each state, there have been at least 22 shooting incidents in which four or more people were shot.