A wise political doctrine known as subsidiarity holds that public-policy challenges should be assigned to the lowest level of government able to address them, thereby ensuring maximum democratic participation in problem solving and the greatest opportunity to tailor solutions to genuine local needs. While some issues – for example, a national highway or rail system – require national-level problem solving, many key challenges of sustainable development are best confronted at the urban level.
被称为辅助性原则（subsidiarity）的政治思想认为，公共政策挑战应该分派给能解决挑战的最低层次的政府，从而在问题解决过程中确保最大化的民主参与，最大限度地让解决方案切合真正的地方需要。一些问题——比如全国高速公路或铁路系统——要求国家层面的问题解决机制，但许多可持续发展方面的重要挑战更适合在城市层面解决。