Why do firms tend to locate near other firms? Economists suspect that geographic clustering spurs innovation by letting businesses tap a climate rich in informal transfers of knowledge. By tracing links between inventors filing for patents for the same inventions, Jeffrey Lin shares new evidence...

Densely populated areas tend to be more productive. Of course, the cost of living and producing in these locations is higher because congestion raises the cost of scarce fixed resources such as land. But despite the higher prices, many people and businesses continue to live and work in these...

Economists believe that people choose to live and work at sites that have productive or amenity value such as a river, harbor, or some other natural resource. Another factor that may determine the location of a city is the benefits derived from density itself: agglomeration economies. Although...