For over a century, doctors have used electrocardiograms (EKGs) to render the invisible electrical activity of the human heart visible, using the pulse to diagnose disease before it becomes fatal. Now, scientists have invented a way to do the exact same thing for the places where most of humanity lives: cities.
In a recent study published in the Proceedings of the National Academy of Sciences (PNAS), researchers have introduced the concept of the "Urban Pulse." By using dense, high-frequency satellite imagery, the team has successfully tracked the dynamic, real-time metabolic activity of urban environments, effectively measuring the heartbeat of a city.
Zhe Zhu, director of the Global Environmental Remote Sensing (GERS) Laboratory and associate professor of natural resources and the environment in the College of Agriculture, Health and Natural Resources ( CAHNR ), was the first author, in close collaboration with senior author Karen C. Seto, the Frederick C. Hixon Professor of Geography and Urbanization Science at the Yale School of the Environment, alongside Michail Fragkias of Boise State University and a multi-institutional team of researchers.
"For decades, we had just been capturing the outcome of urbanization – a house that's been built, or a road expansion," Zhu says. "But you don't really see the dynamics within an urban area."
A city's pulse is determined by all construction activity within the city including new construction, repairs, infrastructure improvements, or expanding into green spaces.
Urban pulse can provide policy makers with a new kind of diagnostic tool to tell them if and where their city is not doing well. This would allow them to be proactive rather than conducting a metaphorical autopsy after the decay of an area is evident.
Historically, planners and scientists have relied on aggregated, infrequent data to study urbanization. The Urban Pulse framework changes this by analyzing decades of dense time-series data from the NASA Harmonized Landsat and Sentinel-2 (HLS) datasets to measure physical transformations like new construction, infrastructure improvements, and demolition at the neighborhood level based on a deep-learning and time-series-analysis approach called CAPES developed by former UConn postdoctoral researcher Ji Won Suh . Suh is currently tenure-track assistant professor at the University of Victoria, Canada.
By observing these high-frequency rhythms of development from space, this new framework bridges the gap between abstract urban theories and measurable, real-world data. Zhu's team looked over many cities and a variety of satellite inputs to develop the urban pulse framework. The paper highlights six cities: Seattle, Shenzhen, Lagos, Mumbai, Dubai, and Mexico City. Despite their vast geographic, economic, and political differences, all six cities shared three distinct "vital signs." Urbanization is: spiky. This means cities do not grow at a smooth, steady pace. Development happens in abrupt, intense, and episodic bursts of construction. They are also cyclical. Neighborhoods go through dramatic boom-and-rest cycles, transitioning through phases of expansion and dormancy that do not follow predictable annual seasons. Finally they are asynchronous. A city does not beat in unison. Different neighborhoods pulse at completely different times, an uncoordinated rhythm that actually prevents the city's infrastructure and labor markets from overheating.
Just as a human pulse reacts to stress or illness, the Urban Pulse can visualize a city's reaction to global shocks. The team's data captured the exact moment the COVID-19 pandemic triggered a widespread, synchronized "cardiac arrest" in urban development worldwide. However, the pulse also revealed profound inequalities in how cities recovered. While places like Shenzhen showed synchronized dips followed by rapid, policy-driven rebounds, cities like Mumbai and Mexico City exhibited entirely different, more muted impacts.
"It's like in human beings," Zhu notes. "When you get a disease, it's not going to show up exactly the same in different people."
The implications of the Urban Pulse extend far beyond academia. For global policymakers, urban planners, and environmentalists, it serves as an early warning system. By monitoring the rhythm, rate, and amplitude of neighborhood pulses, governments can identify early signs of urban decay or unsustainable sprawl and intervene before crises become entrenched.
Furthermore, making this data publicly accessible could revolutionize how everyday people interact with their cities. Citizens considering a move, or entrepreneurs looking to open a business, could simply check a neighborhood's pulse to gauge its economic vitality.
"This is going to be a very impactful tool influencing not only top-down policy decisions from governments but also bottom-up decisions from everyday people navigating their cities," Zhu says.
Zhu completed this work while on sabbatical at Yale University alongside his collaborator Karen Seto.
