brianq, this article divides mass shootings into three types.
https://www.rand.org/research/gun-po...shootings.html
Public mass shootings
Familial mass shootings
Other Felony Mass shootings
What we seem to be most fearful of are the public mass shootings as they seem to be focal point of the discussions here. Oddly enough, those that seem to strike the most fear in us are the rarest of the 3 categorizations. You are more likely to be in a familial event or other felony mass shooting event than in an public mass shooting. Depending on the year, there were more people killed in family events and in other felony events than in public events, but in some years, public events prevailed, but less frequently.
The family aspect is interesting and sort of follows the pattern of violence seen in non-mass shootings whereby you are more likely to be murdered by a family member or person known to you than by a stranger.
I know folks like to talk about "school shootings" but even these are not so simple. You have seemingly random mass shootings at schools where the shooter has no affiliation with the school, but most school shootings seem to be targeted or revenge sorts of shooting. Others, are employee-based just like any other workplace mass shooting, only it happened in a school instead of a post office, lawnmower plant, etc. by a disgruntled employee. In other words, the location doesn't define the motivation despite the fact that we often classify by location.
Some mass shootings are "kill everybody" sorts of mass shootings and some are "kill specific people" mass shootings. There are just many ways these can be broken down.