 While people get really worried about urban pig farms ruining the neighborhood, that kind of thing, market forces lead to a natural separation of uses. Even when it is legal to go and build things next to other things where people wouldn't want them, it rarely happens. There's a reason why most manufacturing is right next to harbors and train stations. That's because you want to get low transportation costs. There's a reason why most commercial construction is on main roads, because you want to get drive-by traffic.