what cities are "red light districts " in?

Apparently the term originated with the practice of the
practitioners of the art hanging red lamps in the window when open for business. A "red
light district" usually refers to an area where prostitution is tolerated. While
prostitution is illegal in most states, it is still  the world's oldest profession, and
does not seem to anywhere near eradicated (or even limited).  The term is usually used
to loosely define an area, and is not confined to cities.