On the number and size of cities*
研究多区域经济中贸易成本下降如何影响产业的空间分布，发现当城市数量不变时，不同规模的城市在不同贸易成本下会收缩，且存在先集聚后分散的稳定均衡路径。
We study the effects of a decrease in trade costs on the spatial distribution of industry in a multi-regional economy, when a rise in the regional population of workers generates higher urban costs. When the number of cities is unaffected by falling trade costs, small cities become smaller for large trade costs, medium-sized cities for medium values of trade costs, and large cities for small trade costs. Furthermore, when urban costs are identical across cities,there exists a path of stable equilibria such that the industry, first, experiences progressive agglomeration into a decreasing number of cities and, then, dispersion into a growing number of cities.