With 80% of Europeans living in urban areas, cities hold the key to sustainable development, said Commissioner Margot Wallstr�m, outlining her "vision" for sustainable cities at the opening session of Brussels' Green Week event. While the EU does not have direct competence in urban affairs, its sectoral policies in the areas of transport, environment and social affairs can have a significant impact on challenges posed by cities. EU ministers responsible for urban and spatial development laid the foundations for a European urban policy on 24 May 2007 with the signature of the Leipzig Charter on Sustainable European Cities Margot Wallstr�m, Commission vice-president in charge of communications policy, outlined the Commission's vision for sustainable cities on 12 June 2007. "The quest for a sustainable future will be lost or won in our urban areas," Wallstr�m said, outlining three reasons why "a shared vision" on urban policy was needed at EU and global level: With cities expanding rapidly worldwide, urban issues will increasingly monopolise attention from governments, encouraging local participatory democracy. More than half of urban areas that will exist across the world in 2030 are yet to be built. "This means that�the world's cities are largely a blank canvas that should be painted, planned, designed and built," Wallstr�m said, adding it is "an amazing chance". Cities "are economic engines", accounting for 80% of the world's economic growth. Building sustainable cities cannot be done by governments alone, Wallstr�m stressed. But she said that governments needed to mobilise citizens and businesses into new forms of partnerships in order to achieve this aim.