Rap music first appeared in New York in the 1970's. Later it spread to large cities with vibrant African American populations - such as Los Angeles, Oakland , Chicago , Philadelphia , and Detroit- without being absorbed by the smaller cities and rural areas in between. Finally, rap music diffused to smaller towns around big cities. This type of spatial diffusion is called * 1 point Relocation potential Hierarchical diffusion Contagious diffusion Cultural diffusion Cascade diffusion