How polycentric is a monocentric city? Centers, spillovers and hysteresis
研究了柏林1890-1936年间交通成本下降和产业转型中，企业选址如何受历史CBD和集聚经济影响，发现企业间溢出效应翻倍使生产率提升从3.5%增至8.3%，并出现多个微集聚区，但城市仍呈单中心形态，体现历史中心的滞后效应。
We assess the extent to which firms in an environment of decreasing transport costs and industrial transformation value the benefits of proximity to a historic CBD and agglomeration economies in their location decisions. Taking a hybrid perspective of classical bid-rent theory and a world where clustering of economic activity is driven by between-firm spillovers, Berlin, Germany, from 1890 to 1936 serves as a case in point. Our results suggest that the average productivity effect of a doubling of between- firm spillovers over the study period increases from 3.5% to 8.3%. As the city transforms into a service-based economy, several micro agglomerations emerge. Their locations close to the CBD still make the city look roughly monocentric. This is in line with a hysteresis effect in which second-nature geography drives the ongoing strength of a historic city center even though the importance of the originally relevant first-nature geography has vanished.