The 'modern town planning' you talk about is so called Euclidan zoning (named so from the town of Euclid in US where it was supposedly first introduced - as a way to segregate rich from poor in an indirect way). Not all areas/countries use such laws. Some time ago this link hit the front page of HN: http://urbankchoze.blogspot.com/2014/04/japanese-zoning.html - it is really an interesting read (other articels on the site as well)