Despite decades of suburbanisation, modern cities continue to be anchored by highly concentrated hubs of economic activity. In a new study, Gabriel M. Ahlfeldt (HU-Berlin, Project B10), Thilo N. H. Albers (University of Münster), and Kristian Behrens (Université du Québec à Montréal) develop an algorithm to delineate what they term “prime locations”: ultra-dense clusters of economic activity that act as dominant centres of economic gravity within cities. By applying their method to georeferenced establishment data, the authors mapped 531 prime locations across 381 US metropolitan statistical areas. To address regions where administrative data are sparse, they designed a predictive model using web-scraped business locations and Google Places data, allowing them to map 286 prime locations across 125 global cities in 35 countries.
The findings reveal a striking degree of spatial concentration, particularly within the tradable services sector. Many large US and global cities concentrate more than one-third of their tradable services employment on less than 0.3 percent of developable land. For example, Midtown Manhattan (the most extreme case documented) hosts 1.71 million jobs within just 11 square kilometres, representing an employment density of 156,000 workers per square kilometre.
Crucially, the study demonstrates that most cities are remarkably mono-centric or duo-centric, with nearly 70 percent of global cities and over 90 percent of US metropolitan areas containing only one or two dominant employment centres. The authors uncover a subadditivity property of urban hubs: as the number of prime locations within a city increases, their collective share of total citywide employment actually falls. For instance, Los Angeles, with nine separate prime locations, concentrates less than 10 percent of its citywide employment within them, whereas New York’s two prime locations concentrate about 25 percent. This suggests that dividing workers across multiple hubs dilutes localised agglomeration economies and reduces the unique productivity benefits of face-to-face knowledge exchange.
The research also links these spatial configurations to historical infrastructure. Cities with older mass transit systems are significantly more mono-centric today; introducing a subway system a century ago is associated with having nearly one fewer prime location and a much higher concentration of employment in the remaining hubs. Ultimately, these prime locations serve as powerful gravity wells: while commercial real estate investments, building heights, and office densities plummet immediately outside their boundaries, residential population densities remain flat, proving that these hubs are distinct engines of commerce rather than simple reflections of general urban density.
Link: Prime Locations
