The Fragmentation of Urban Footprints: Global Evidence of Sprawl, 1990-2000

Cities the world over are highly fragmented. The fragmentation of the built-up area cities
by the open spaces interpenetrating them is a key attribute of urban-sprawl, and sprawl as
fragmentation, as distinct from sprawl as lower-density development, is now a universal
feature of cities. Using satellite images and census data for 1990 and 2000 for a global
sample of 120 cities, we find that cities typically contain or disturb vast quantities of open
spaces, equal in area, on average, to their built-up areas. That said, we find that
fragmentation, defined at various spatial scales as the relative share of open space in the
urban footprint as a whole or in parts of it, is now in decline. We use multiple regression
models to explain variations in fragmentation and in its decline among cities and regional
groupings. We find that larger cities are less fragmented; that high levels of car
ownership tend to reduce fragmentation, possibly because they allow infill at relatively
low costs; that there were parallel declines in average built-up area densities and in levels
of fragmentation during the 1990s; and that cities that do not permit development in large
areas around are slightly, yet significantly, less fragmented. Policies aimed at reducing
fragmentation should be clearly distinguished from policies aimed at increasing the
density of built-up areas. Encouraging infill in cities with little population growth is
qualitatively different from encouraging infill in cities with rapidly growing populations.
In the former, it can form the backbone of an effective ‘smart growth’ policy. In the
latter, it is overshadowed by the urgent need to prepare vast areas for projected outward
expansion.