the same characteristics that make cities socially and economically progressive spaces also generate complex environmental and social challenges that can only be met by active public interventions at multiple scales at the household eg housing subsidies city eg planning and national levels eg trade and employment policies if these challenges arc not dealt with effectively the welfare of individuals communities and entire nations can suffer these are no inevitable consequences of rapid urban population growth rather they are a consequence of political and institutional failure that inhibits effective urban planning policymaking investment and regulation