Urban Skylines: building heights and shapes as measures of city size

TL;DR

This study analyzes over 4.8 million buildings across North American cities, revealing how building heights and shapes scale with city size and impact energy efficiency, highlighting heterogeneity in urban form and energy considerations.

Contribution

It provides the most extensive dataset analysis linking building shapes to city size, confirming theoretical scaling laws and exploring energy implications of shape variations.

Findings

Average building height increases with city size.

Higher buildings tend to have lower surface-to-volume ratios.

Downtown cores exhibit more needlelike, energy-inefficient shapes.

Abstract

The shape of buildings plays a critical role in the energy efficiency, lifestyles, land use and infrastructure systems of cities. Thus, as most of the world's cities continue to grow and develop, understanding the interplay between the characteristics of urban environments and the built form of cities is essential to achieve local and global sustainability goals. Here, we compile and analyze the most extensive data set of building shapes to date, covering more than 4.8 million individual buildings across several major cities in North America. We show that average building height increases systematically with city size and follows theoretical predictions derived from urban scaling theory. We also study the allometric relationship between surface area and volume of buildings in terms of characteristic shape parameters. This allows us to demonstrate that the reported trend towards higher (and more voluminous) buildings effectively decreases the average surface-to-volume ratio, suggesting potentially significant energy savings with growing city size. At the same time, however, the surface-to-volume ratio increases in the downtown cores of large cities, due to shape effects and specifically to the proliferation of tall, needlelike buildings. Thus, the issue of changes in building shapes with city size and associated energy management problem is highly heterogeneous. It requires a systematic approach that includes the factors that drive the form of built environments, entangling physical, infrastructural and socioeconomic aspects of cities.