zoning restrictions arises because of the presence of external effects in the urban property market. In other words, if one happened to own a house in an exclusive r sidential district, the possible location of a glue factory, beer joint, or even a gasoline service station on the adjacent lot would no doubt be upsetting since possible odors, noises, congestion, etc., might act to lower the value of the residence. In fact, all zoning restrictionsuse, height, area, and density regulations -can be viewed as an effort to eliminate