Urban Conversations | A City Is Sometimes a Tree

In his seminal 1965 article “A City Is Not a Tree,” design theorist Christopher Alexander argued that urban planners—working centrally and top-down—tend to design cities as efficient hierarchical tree-like structures, whereas successful traditional cities evolved naturally as messy interconnected lattice structures. Alexander’s claim was at once both descriptive and normative: (successful) cities are not trees, and planners should not plan cities as trees. His paper became an influential landmark across the fields of urban design, transport planning, complex systems, and network science. This talk reconsiders this claim empirically and argues that “successful” cities are, in fact, very often very tree-like. It theorizes this in terms of the real-world trade-offs between infrastructure networks’ structural redundancy and cost, and how these trade-offs constrain urban form. Finally, it considers what this means for how we plan cities for more connected, sustainable futures. 

Registration is required for this event. Lunch will be provided.

Speaker: Geoff Boeing is an Associate Professor in USC’s Department of Urban Planning and Spatial Analysis, the Director of USC’s Urban Data Lab, and a Nonresident Senior Fellow at the Brookings Institution. His research and teaching focus on geospatial data science, urban networks, and information landscapes. His work has won the Nobel Sustainability Award and the Stough-Johansson Springer Award, and is regularly featured in the media including The Economist, The Guardian, The Atlantic, and The Washington Post. He developed and maintains the OSMnx street network modeling software and has served as a consultant for several planning, policymaking, and public health organizations. He has never played a round of golf or drunk a cup of coffee in his life.

Discussant: Carole Voulgaris is Associate Professor of Urban Planning at Harvard University Graduate School of Design.

This event is co-sponsored by the Center for Geographic Analysis.

About the Series

As our planet becomes increasingly urban, this series seeks to expand our understanding of cities and urbanization across sites and scales. The Urban Conversations aim in particular to link humanistic approaches with spatial investigations. We host public talks, and provide a venue for researchers to share works-in-progress with an interdisciplinary community, in a conversational format. Urban Conversations is chaired by Bruno Carvalho and Daniel Agbiboa.