The metropolitan area of Brussels (i.e. the study area) has about 2.9 million inhabi-tants. Its central part, which corresponds to an administrative entity, the Brussels-Capital Region, groups a little less than 1 million inhabitants, but the actual morpho-logical agglomeration spreads beyond the limits of the Region. Beyond the suburbs, further in the hinterland, some medium-size secondary cities (Aalst, Leuven, Mech-elen, Louvain-la-Neuve among others) are lying, which function more autonomously from Brussels.

The spatial structure of Brussels itself (the city) is quite typical. An old industrial axis along a canal surrounded by poor neighbourhoods of different ethnic communities with very few green spaces makes its way through the whole city, cutting it in two parts. Neglected during decades this area slowly begins to be renovated. On the other hand, the strong increase of administrative functions in the nineties introduced a speculative pressure on higher status neighbourhoods, making the cost of living increase. Out-migration of middle class families to the suburbs encouraged urban sprawl, commuting by car and traffic congestion on the access roads to the city. On the other hand, in the Brussels-Capital Region, the decline of population and the lowering of its average income increased the scarcity of the resources of the local authorities, essentially based on income taxes of residents, while a lot of public works must be done to adapt this central area to the increasing administrative functions.

On the whole metropolitan area, population and jobs globally increased between 1991 and 2001 (respectively by 3.7 % and 12.1 %), generating an increased con-sumption of space : the total built area increased by 18.1 % in the same period. Still in that period, the population density in the residential areas decreased and the land consumption per inhabitant increased from 1.65 ares to 1.89 ares. A crucial issue is whether such a high urbanisation rate is sustainable for the metropolitan area.