Our paper “The Complexity of Urban Verticality” has been accepted for publication in npj Complexity, the Nature Portfolio journal dedicated to complex systems. Kudos to lead author Benny Chin (Wei Chien Benny Chin, now at the Department of Geography, National University of Singapore), a former Research Fellow of the group, who carried this work from the first idea to the accepted manuscript. The paper is co-authored with Michael Lees (Informatics Institute and Institute for Advanced Study, University of Amsterdam).

As cities increasingly grow in three dimensions, their vertical structure has become an important yet under-examined component of urban form. The paper introduces a spatial scaling framework that characterizes urban vertical complexity directly from Digital Surface Model and Digital Terrain Model data. A hierarchical quadtree representation generates a Total Absolute Difference (TAD) profile across successive scale levels, and the slope of the profile’s tail serves as the principal metric for comparing places. The framework is tested on nested windows in Canary Wharf, on 192 one-kilometer windows across three London zones, and on 17 standardized urban-zone windows in England. Across these analyses the TAD profiles share a shallow head followed by a steeper tail, with most of the variation in the tail regime; the tail slope is related to the tallest buildings but is not reducible to height alone. The result is a quantitative way of comparing how vertical structure is organized across different urban landscapes.

The Complexity of Urban Verticality
Chin WCB, Lees MH & Bouffanais R
npj Complexity, accepted for publication, 2026. [pdf]

Our Ph.D. student Arthur Rondeau has posted a new preprint on arXiv, together with Alain Barrat (Aix Marseille Université, CNRS, Centre de Physique Théorique). When all we observe is a system’s dynamics — for instance a sequence of visited nodes — how can we tell whether group (higher-order) interactions are really at play, or whether pairwise interactions suffice? Group interactions leave a trace as memory in the observed sequence, but a memory-driven pairwise process can mimic that same footprint. The paper introduces an inference pipeline built on a hidden Markov model whose latent states are the hyperedges of an unobserved hypergraph, turning the question into a falsifiable model-selection test against memoryless and memory-based pairwise baselines. Applied to ball-possession trajectories from professional football matches (StatsBomb open data), the recovered hyperedges map directly onto recognizable tactical team formations.

Uncovering Higher-Order Interactions from Memory in Observed Dynamics
Rondeau A, Barrat A & Bouffanais R
arXiv preprint arXiv:2610.20095 [cs.SI], October 2026. [pdf] [arXiv] [doi]

Our new preprint introduces IntLawNER, a named entity recognition dataset and benchmark for international law.

IntLawNER: A Named Entity Recognition Dataset and Benchmark in International Law
Skura G, Bouffanais R & Wernli D, arXiv preprint arXiv:2609.22529 (2026).

[pdf] [doi] [web]

The Science in Diplomacy Lab (SiDLab) publishes its first policy report, the outcome of a collective effort by 21 co-authors from Geneva and partner institutions. The report sets out why effective multilateralism needs a data-driven and complexity-aware digital infrastructure, and what building one would entail for international organizations, member states and the research community.

Building a Data-Driven and Complexity-Aware Digital Infrastructure for Effective Multilateralism
Vanackère F, Boggio A, Escher G, Evrard M, Faude B, Gomis M, Kaspiarovich Y, Kim RE, Lees M, Legara EFT, Lo Russo N, Ruhl JB, Sandoval K, Sauser J, Scherer DS, Seidler N, Santos Domínguez AB, Wolf N, Levrat N, Bouffanais R & Wernli D
Science in Diplomacy Lab Policy Report No. 1, Geneva, June 2026. [pdf] [web]

Using U.S. diplomatic communications, our new preprint shows how hypergraph representations reveal higher-order interactions in complex networks.

Revealing Higher-Order Interactions in Complex Networks: A U.S. Diplomacy Case Study
Rondeau A, Wernli D & Bouffanais R, arXiv preprint arXiv:2509.10333 (2025).

[pdf] [doi] [web]