It's not wrong but what people usually want to know looking at crime stats map is a probability to become a victim if they visit a particular place of will more to live there. Crime count divided by number of residents only relevant for crime targeting residents like home burglaries. For other cases these number can be no-representative.
It should really be crime count by number of people out and about a day, but you will never have that number without some orwellian citizen surveillance program.