This is a city metric I haven't seen before. City Observatory recently looked at the number of police officers (public) and security guards (private) per capita across American cities. They also ask a bunch of interesting questions. Why do some cities have far fewer police officers? Is high security an indicator for "anti-social capital?" (Social norms aren't encouraging people to behave.) And do some cities simply have more cops because it is perceived to be necessary?

Here is what they found:

The average is about 3.3 police officers per 1,000. And in each case, city is defined as the metro area. The study relies on census data and, if we're being precise, the data represents where people live as opposed to where they work. So some cities could be reporting a lower number simply because police officers tend to live outside of the metro area -- perhaps because of housing costs. Either way, it's interesting to consider why some cities spend a lot more on security than others and why Miami has so many security guards.

Chart: City Observatory