Anatomy of density: measurable factors that constitute urban density

Serious concerns about global warming have been translated into urgent calls for increasing urban densities, as higher densities are associated with lower carbon emissions from both vehicles and buildings. However, attempts at effective densification have generally failed and urban densities continue to decline in cities across the world. Calls for densification without making room for it have resulted in serious housing supply bottlenecks in many cities and have rendered their housing unaffordable. If affordable densification is to be successful, it is necessary to understand the factors that constitute urban density. A novel way is presented for factoring the average density of cities into constituent factors—three or seven factors—that when multiplied together reconstitute urban density. This factoring methodology is presented together with the preliminary measurement of these factors in 10 cities in 10 world regions. This approach allows, for the first time, a clear understanding of how different cities acquire their density: Hong Kong gets its density from building height; Kinshasa from crowding; and Dhaka and Bogotá from residential coverage. This anatomy of density offers a new outline for a comprehensive strategy for city densification: one that addresses each and every one of the factors that constitute urban density. Practice relevance Urban density is usually defined as the ratio of the total population of a city and its total area. This is the most appropriate single metric for measuring progress in densification in cities and is now a central objective of the global climate change agenda. However, this metric is rather crude and often hides more than it reveals. The anatomy of density offers a new, simple method for factoring urban density into its constituent factors that when multiplied together reconstitute urban density. This approach offers city leaders and urban planners a new way to consider and develop comprehensive policy options and strategies for city densification that addresses each and every one of the factors that constitute urban density and the tradeoffs between them.