Currently, over 50% of the world's population lives in urban areas. By 2050, this estimate is expected to be 70%. This urban growth, however, is not uniformly distributed around the world. The majority of it will occur in developing nations and create megacities whose populations exceed at least 10 million people. Not all urban areas, however, are growing. Some are actually losing populations because of changing economic conditions and population demographics. Whether a city is growing or losing population, governances face unique challenges with respect to infrastructural, water and transportation needs. To meet these challenges, agencies within city government are cooperating by pooling resources and removing conflicting policies, partnering with the private sector to offset costs of infrastructure, and taking new approaches to design infrastructure. By linking ecological theory with urban design, a more integrative approach to create liveable spaces, which are sustainable, can be achieved in rapidly expanding and shrinking urban areas.

Key Concepts:

• Megacities and shrinking cities are our future. In the nineteenth and twentieth centuries, most of the world's population lived in rural areas. With economic shifts people moved into cities to find employment, better health services, and improved education opportunities.
  
• Future cities represent major ecological, social and economic challenges and opportunities. Rapid urban growth creates economic incentives but can fragment, destroy or degrade existing natural ecosystems. Similarly, population losses create economic and ecological opportunities for expansion and growth.
  
• Integrating ecological theory in urban design can create a framework for sustainable cities that are adaptive and resilient. Often, infrastructure is designed to meet engineering specifications but do not incorporate ecological functionality. By integrating ecological with the engineering, infrastructure can meet regulations at the same time enhancing the environment.