The maps lack normalization by population density. But even that might be misleading, for example industrial areas having low population densities but nonetheless a lot of people in the area during working hours. And while population density might be relevant for some crimes it might be irrelevant for others. Where not to park your car is probably better normalized by the number of parking spaces or even the number of cars present. So don't try to read to much out of maps or charts not specifically crafted to answer the question you are interested in.