Most maps using count of reports of crime end up being maps of the population density of cities. An attractive response would be to turn these counts into a rate, but a rate per what?
Most commonly, people seem to divide the counts by the population number from the census.
However, that's more or less a count of where people sleep. In most American cities, relatively few people live in the Central Business District, and it doesn't seem to make a lot of sense to divide by that number for that area. Most homicides in my city are of minority, male youth between the ages of 15 and 30. Should I divide by the total population or try to identify the population who's at risk?
Maybe there are two questions: 1. if you had a magic wand, how would you normalize crime reports, and 2. how in practice have people solved this problem?