In a groundbreaking study published in the prestigious Proceedings of the National Academy of Sciences, researchers from the Complexity Science Hub (CSH) have unveiled a remarkable pattern underpinning the economic evolution of U.S. cities over the past 170 years. Their work reveals that despite sweeping transformations and diversification in urban economic activities, cities maintain a surprisingly consistent level of “coherence,” a complex metric that captures the structural harmony of economic functions within urban environments. This discovery sheds new light on the dynamics that constrain urban economic development and offers profound implications for the future of city planning and policy.
The study meticulously analyzed a vast and unique dataset encompassing over 650 million U.S. census records, more than 6 million patents, and a trove of historical documents. This comprehensive approach allowed the researchers—Simone Daniotti, Matte Hartog, and Frank Neffke—to explore nearly two centuries of urban economic history, delving deep into the shifts from craftsmanship and manufacturing-based economies toward service and engineering-dominated cities. Using advanced data analytics and statistical modeling, the team quantified how cities adapt their industrial compositions while retaining an underlying structural logic that balances diversification with inter-industry coherence.
Central to their findings is the concept of coherence, which operates as the economic “glue” binding the diverse activities within a city. According to Daniotti, coherence is a multifaceted measure that takes into account three key dimensions: the breadth of distinct economic activities present, the relative balance of these activities across the city’s workforce, and the degree of relatedness or similarity among these activities. In effect, coherence reflects not just diversity but how well the economic activities fit together, enabling productive interaction and mutual reinforcement. Cities with high coherence tend to have concentrated, tightly connected industries, much like Detroit’s historic automotive sector, whereas less coherent cities, such as contemporary New York, span many unrelated sectors, resulting in a more fragmented economic fabric.
One of the most intriguing aspects of the research is the discovery that despite major structural changes, cities’ coherence levels remain remarkably stable over time. This constancy suggests that economic transformations are fundamentally constrained by the need to maintain an internally consistent set of capabilities. Cities innovate and branch out, but they do so within a framework that avoids disrupting the cohesion of their economic ecosystems. Neffke explains that this constraint likely arises from the embedded physical, institutional, and human capital infrastructure, which supports existing industrial arrangements and must be maintained for successful transitions.
The study also highlights fascinating regional dynamics, particularly comparing the economic evolution of East Coast and West Coast cities. While the East Coast embodies the traditional arc of U.S. urban development, the West Coast manifested a more accelerated and pronounced structural shift. Beginning with nascent cities like San Francisco and Los Angeles emerging from the Gold Rush era, the West Coast rapidly diversified its economic base. Within just fifty years, these cities expanded their export-oriented occupations to nearly 90% of those prevalent nationwide. Despite this rapid diversification, West Coast cities managed to uphold levels of economic coherence on par with their older eastern counterparts, emphasizing that swift change does not necessitate fragmentation.
Crucially, the researchers found that city size plays a pivotal role in coherence dynamics. Larger urban centers consistently exhibit lower coherence, with the metric declining at approximately 4% per each doubling of population. This scaling law underscores a universal principle in urban economics: bigger cities harbor greater diversity, but this comes with a trade-off in structural cohesion. The finding also implies that as cities grow, their economic systems become more complex and heterogeneous, yet the relative decline in coherence suggests there are natural limits to how diverse a city’s economy can become without losing essential interconnectedness.
From a policy perspective, these insights furnish critical guidance for urban economic development strategies. The researchers caution against unchecked diversification ambitions, emphasizing the necessity for cities to preserve a core level of coherence to harness existing capabilities effectively. As Neffke notes, a city’s economic capabilities are embedded in costly infrastructure, specialized labor pools, and institutions that cannot be infinitely stretched. Thus, urban policymakers must balance innovation and expansion of new sectors with the imperative to maintain an internally consistent economic fabric that fosters resilience and sustainability.
Further complicating this balancing act is the fact that larger cities possess the advantage of supporting a wider array of activities due to their scale, affording them greater flexibility in diversification. However, this advantage is bounded by the steady scaling relationship between population size and coherence. Recognizing these universal regularities underscores the importance of benchmarking cities against size-comparable peers, enabling more realistic expectations regarding diversification goals and economic transformation pathways.
The study also delves into historical examples such as Pittsburgh and Boston, cities that confronted steep industrial declines yet orchestrated successful economic recoveries by strategically transitioning out of heavy manufacturing into high-tech and service-oriented sectors. These transformations exemplify how cities must carefully navigate shifts in their industrial bases without compromising coherence, underscoring the challenges of reorienting urban economies while maintaining structural integrity.
Technological evolution over the examined period—from the age of railroads and telephones to the digital revolution and artificial intelligence—has radically reshaped urban economies. Yet, remarkably, the relationship between city size and economic coherence has remained stable. This suggests a deep, underlying rule governing urban economic systems, transcending specific technologies or historical epochs. It highlights that urban economies are bound by fundamental constraints that govern how diverse and coherent their industrial compositions can be.
The research advances not only theoretical understanding but also practical tools for urban planners and economists. By using measures of coherence, stakeholders can identify which economic activities constitute the “capability base” of a city and which can be developed or pruned without risking structural fragmentation. This nuanced understanding is essential for guiding investments, workforce development, and infrastructure planning, particularly in an era characterized by rapid technological progress and shifting economic landscapes.
Ultimately, the study by Daniotti, Hartog, and Neffke redefines how we comprehend the evolution of urban economic systems. It challenges the simplistic narrative that cities simply diversify endlessly and instead reveals a sophisticated image of economic change constrained by enduring structural principles. This insight is not only academically profound but also urgently practical in shaping the future trajectories of U.S. cities as they navigate the complexity of modern economies in the twenty-first century.
Subject of Research: People
Article Title: The coherence of US cities
News Publication Date: September 23, 2025
Web References:
Proceedings of the National Academy of Sciences Article
References:
Daniotti, S., Hartog, M., & Neffke, F. (2025). The coherence of U.S. cities. Proceedings of the National Academy of Sciences.
Image Credits:
Complexity Science Hub
Keywords:
Cities, Urban planning, Urbanization, Economics, Economics research, Public policy, Economic geography, Economic history
