This is super tricky. One project I worked on looked at pedestrian deaths at a regional scale. We were lucky that the regional government had daytime population

This is super tricky. One project I worked on looked at pedestrian deaths at a regional scale. We were lucky that the regional government had daytime population estimates for the CBD. Otherwise downtowns tend to look like pedestrian killing fields. Even with those daytime estimates, you're stuck treating those areas as "special," and thus limiting yourself in terms of the kinds of comparisons you can defensibly make. You don't always need to supply a rate to get a useful visualization either. In the case of pedestrian fatalities, you might still want to invest heavily in safety improvements where absolute numbers of fatalities are high, but rates are low. On the visualization side, I've found that maps are not always the best strategy for spatial data.