Some planners and economists once built a model of their city. They assumed all the jobs were downtown and people wanted to minimize the combined cost of housing and commuting. How far, on average, would people live from work?
The model said, “One mile.” But census data showed that people actually lived an average of seven miles from work.
The planners and economists had totally opposite responses to this answer. The economists assumed there was something wrong with the model, and set about refining it. Instead of a monocentric model in which all jobs were downtown, they created a polycentric model that spread jobs across several different job centers. The revised model said people would live a little more than two miles from work.
“Naturally we don’t expect the real world to fit the model perfectly,” wrote the economists, “but being off by a factor of seven or even three is hard to swallow.” The economists concluded that the model needed much more refining.
