Why do competitors open their stores next to one another?

I often wondered why the crowd of computer shops exist only at one place in our city; why all those big garment showrooms open next to each other; or even why all the shops of musical instruments open only at one place (and those at other places get closed).

This video answers that well, in a simple animation.

Link: http://www.youtube.com/watch?v=jILgxeNBK_8&feature=share