Spatial analyses of cities have so far mainly provided much insight into the expansion of built-up areas within cities. Changes within these built-up areas have been largely ignored. As a result, the extent of urban change often remains unknown.
Building-level changes
Job Rosier, Vita Bakker and Jasper van Vliet (Vrije Universiteit Amsterdam) and Elizabeth Wamuchiru (University of Nairobi) therefore investigated building-level changes in Nairobi between 2010 and 2021. Using very-high-resolution imagery, they manually mapped whether buildings appeared, persisted, changed, were replaced or demolished. They linked these changes to urban development processes. The study was published in the International Journal of Urban Sustainable Development.
The researchers found that as much as 29 per cent of the built-up area has been demolished, replaced or renewed. "We see that these changes are systematically changing the structure of the city," says Van Vliet. "New buildings are larger than buildings that disappear or are replaced. Also, new buildings are more regular - relative to their neighbours - than buildings that disappear or are replaced.
Underlying processes
The results show important underlying processes, such as the disappearance of slums and the densification of cities. Van Vliet: "These processes have a major social impact, and should therefore be studied more systematically."
The research shows that building-level change analysis offers a new possibility to study the dynamics of cities. This is especially relevant in rapidly changing cities in the Global South, where much more changes in a decade than in cities such as Amsterdam.
