Addressing the determinants of built-up expansion and densification processes at the regional scale

Blog by Ahmed Mustafa, Anton Van Rompaey, Mario Cools, Ismaïl Saadi and Jacques Teller

7 Feb 2018, 9:59 a.m.
Ahmed Mustafa, Anton Van Rompaey, Mario Cools, Ismaïl Saadi and Jacques Teller



Urban sprawl constitutes a significant environmental, economic and social challenge across the globe. Policies have been developed to curb this phenomenon and foster a more efficient use of the land. Such policies are typically based on a combination of spatial planning with fiscal and economic measures, promoting infill development and land recycling. Infill development is targeting low- and medium-density urban areas, with significant capacities in terms of available land and existing services (access to transport, urban amenities etc.). It is especially required in regions like Wallonia (Belgium), where low densities and significant discontinuities with historical urban cores characterize a number of built-up areas.



Fig.1 Classification of built-up cells in 2010 (Liege, Belgium).


This paper compares the strength of controlling factors governing urban expansion (i.e. sprawl) with the ones governing densification processes (i.e. infill development). To this end, urbanization in Wallonia was analyzed using a regression model that compares the status of cells (non-urban, low-, medium- and high-density) from 1990 to 2000 and from 2000 to 2010. The maps are based on datasets derived from cadastral data.


Our analysis shows that the transition from non-urban to low-density developments keeps largely dominant in urbanization processes in Wallonia. However, a progressive shift toward infill development, namely a densification of existing built-up areas, can be observed in the second study period (2000-2010). This shift can be related to recent spatial policies. Since 2005, the definition of a new zone to be urbanized in the regional zoning plan in Wallonia must be compensated by the downzoning of a similar-sized area that was to be urbanized beforehand to a nonurban zone.


The research further reveals the main factors triggering low-density developments. Spatial planning —i.e. zoning status— keeps the main factor governing urban sprawl in Wallonia. Road accessibility and neighborhood interactions are two other determinants of low- and medium-density developments. On the other hand densification processes are largely driven by proximity to already dense areas. Densification is not related with proximity to railway stations, which means that infill development does not follow a transit-oriented development approach in Wallonia. Proximity to medium- and large-sized cities does neither appear to be a key factor in densification processes, even though it is certainly where infill development is most expected in terms of both real estate value and contribution to sustainable development (compact city). This phenomenon may be related to the fact that densification appears highly correlated with neighborhood characteristics, which may conceal the effect of proximity to medium- and large-sized cities where denser areas are observed.


Contrasting the drivers underlying expansion and densification processes is essential for designing spatial policies that support land recycling. In-fill development, and especially transitions from medium- to high-density development, should further be amplified, especially in those areas that are best located in terms of accessibility to transport and services. In Wallonia, this would require a revision of zoning plans through the transfer of development rights from remote areas towards well-connected places.


Read the paper on Urban Studies - Online First here.



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