Seriously. At what point does correlation become causation?
When you have eliminated the other possible causes. Cum Hoc Ergo Propter Hoc.
In this case Population Density might really be the determining factor, as much as we would like to thinks its lefties, because they prefer to live in densely populated areas to feed their relent narcissism.
Or Gang activity - which is much more prevalent in urban areas ( or perhaps you need a certain population density to form the gangs in the first place - for anonymity for one, and just recruits for a second)
Of Course if the graph were reversed, the lefties would be screaming it was proof Conservatives are more violent,etc. So yeah, screw em- Lefties are the cause of gun violence. Its plain as day.