They are based on safety information published by various local groups. Try to avoid these areas if you are alone. If it is late and you are able to take a cab or bus to your destination, do so. If you must walk alone, walk assertively and be alert. If you are intoxicated, drugged, tired, or upset, try not to show it.
Assailants have a nose for vulnerability and are looking for easy targets.
If you hear someone behind you, don't be afraid or embarrassed to turn around and see who it is. If you feel threatened, you very well may be, and you should act accordingly. Every second of denial reduces the time you might need to escape. If you think someone is following you, widen the distance between the two of you. Walk closer to the street or cross the street.