Most zoning ordinances segregate residential, commercial, and industrial zones.
Planning historian Larry Gerckens tells how this came to be. The physical separation and isolation of dangerous, odoriferous, or unsightly practices, such as tar boiling, soap making, fat rendering and dead carcass cremation, was viewed at that time as a reasonable governmental response to the unacceptable impositions of one otherwise legal activity upon another. Both the residences and these businesses had their right to exist, it was held, but not necessarily in close proximity to each other.