The data for this map was collected by ShootingTracker.com, a crowd-sourced project attempting to track mass shootings. They define a mass shooting as one in which four or more people were injured or killed by gunfire -- which includes domestic situations, shootings during crimes, etc. This is a broader than the definition used by the the federal government.
Click a bubble for more information about that mass shooting.
This, however, does not take population density into account. It stands to reason that with more people comes more mass shootings. For instance, there haven't been any mass shootings this year in North Dakota, Wyoming, New Hampshire, West Virginia or Hawaii, which are all relatively low-population states.
So, we used the most recent state populations to find a per capita rate of incidents for each state and then multiplied by 10,000,000 to get them into somewhat whole numbers. That map is below. The highest rate by population? Washington D.C.
Sources: ShootingTracker.com, plus our own addition of location specificity on shootings in Minnesota. State population data is from the U.S. Census Bureau.