Very interesting.
Safe is a function of who you are, who you are with, time of day and luck.
Generally, the following cities are unsafe: Lima, Peru (after dark), D.F. (Mexico City), Mexico, Rio, Brasil, NYC after dark, Most border towns along the Mexican border, especially after dark.
With that said, I've strolled in DF, no problems, walked alone the streets oh Philly and LA at night alone and no problems. Did have 5 guys try to rob me in Havana however I wouldn't consider it unsafe and they ended up giving up and got nothing. I also was in a Mexican border town and while I got some dirty looks, I was twice their size and in a group so nothing went down.
Latinamerican large cities are bad for women due to the macho attitude that is so prevalent and low prosecution rates of crimes. One only need look at the 100's of rapes and murders in Juarez (Mex. frontera) and the blisters the cops have on their hands for sitting on them.