Who decides what you can build on your own land?

Usually your city does, through zoning: a method in which a government divides land into zones, each with its own rules about what may be built there. A zone can say what you may do on a plot (live, shop, make things), how tall and how big the building may be, and how dense an area can become.

Cities have always sorted land. Ancient walled cities put the smelly and dangerous work, like butchering and brick-firing, outside the walls. But modern zoning was born in a fight over sunshine. New York's Equitable Building covered its entire lot, towered over its neighbours and blocked their windows and light. In 1916 the city adopted the first zoning rules to apply citywide, partly in reaction to it.

Its legality was settled by a 1926 Supreme Court case. The suburb of Euclid, Ohio, had zoned the land of Ambler Realty to keep out industry, and the company sued, saying this took its property. The Court said zoning was a reasonable use of the government's police power. The rule that keeps one use per district is still called Euclidean zoning.

Not every country does it this way. Paris mostly regulates the form of buildings, not their use, and banned buildings over seven storeys in its centre after the Montparnasse Tower caused an outcry. Houston is the biggest US city without zoning, though private deed restrictions do similar work.

The big question is what zoning does to cities. Critics say single-use and single-family zoning cause sprawl, push up prices and entrench segregation. Defenders point to its simple rules, long legal precedent and familiarity, and to its roots in controlling nuisances. Most of the rest of the debate over housing and cities runs through that disagreement.