Livable cities of the future : proceedings of a symposium honoring the legacy of George Bugliarello At the beginning of the 20th century an estimated five percent of the worlds population lived in cities. Today half the worlds population is urbanized. Urban sustainability is multifaceted and encompasses security economics environment and resources health and quality of life. It can be viewed as the intersection of two extremely complex and not yet fully understood processes urbanization and global sustainability which will increasingly overlap as urban populations continue to grow. Effective policies are critical for addressing urban sustainability and must be politically realistic in deciding on appropriate balances such as centralized versus decentralized systems soft versus hard solutions local versus regional focus agriculture versus pollution and free markets versus interventions. Publishers description