PNAS Nexus · Vol 5, Issue 5, 2026 · pgag130
“Knowing that a place is ‘commercial’ or ‘residential’ does not capture what activities take place there, or when and why people go there.”
The Problem
Urban planners and researchers have long tried to quantify how vibrant a city feels — how alive, varied, and energetic its streets and spaces are. Two dominant approaches exist, but both miss something fundamental: what people are actually doing, and how rich and balanced that activity is across time and space.
Counts how many people live or gather somewhere. Treats all presence as equivalent — a rush-hour commuter and a festival-goer register identically, erasing the qualitative texture of city life.
Classifies zones as residential, commercial, or industrial. Captures what a space is designated for — not what unfolds within it at any given hour, or why people choose to be there.
Measures the richness and evenness of distinct human activities — working, shopping, socialising, celebrating, and more — drawn directly from behavioural data rather than planning designations.
“Knowing that a place is ‘commercial’ or ‘residential’ does not capture what activities take place there or when and why people go there to perform those activities.” — Yiu, Pacheco, Di Clemente & Botta (2026)
The Framework
The paper’s central insight is that urban vibrancy behaves remarkably like biodiversity in ecology. Both depend on the same five determinants; both can be quantified with diversity indices such as Shannon entropy; and both face a “carrying capacity” beyond which more is no longer better. By mapping these determinants across three fields — ecology, retail, and urban planning — a unified measurement framework emerges. Click any row to explore the parallel.
↑ Click a row to highlight it
Activity Taxonomy
Rather than labelling spaces by their planning designation, this framework classifies urban behaviour into 13 activity categories grounded in what people actually do — drawn from mobile phone traces, social media data, and behavioural surveys. Measuring the mix and balance of these activities gives a richer, more dynamic picture of vibrancy than any land-use map can provide. Click an activity to explore.
Borrowed from Ecology
One of ecology’s most powerful concepts is carrying capacity: the maximum load an environment can sustain without degrading. The same logic applies to urban spaces — too little activity feels lifeless, but too much tips a neighbourhood into overcrowding, noise, and decline. Vibrancy is not a monotone function of busyness: it peaks, then falls.
Looking Ahead
Turning the biodiversity analogy into a practical urban measurement tool requires new data pipelines, interdisciplinary methods, and careful attention to ethics and representation. The paper maps out both the opportunities and the open challenges.
Data Sources
Behavioural traces that reveal where people go and what they do — capturing temporal dynamics invisible to traditional censuses.
OpenStreetMap, points-of-interest databases, and urban geometry to ground activities in physical space and built form.
Visual assessment of built-environment quality and design — a proxy for the structure and design determinant of vibrancy.
Contextual grounding — essential for understanding how activity diversity intersects with deprivation and demographic inequality.
Key Challenges
Citation
Published open access in PNAS Nexus (Oxford University Press) under CC BY licence.
Funded by the International Central Networks and Partnerships Grant; the Lagrange Project
(CRT Foundation); and the COLINE DUT European Partnership.