There is a debate going on since the beginning of the year regarding the future of housing and the built environment (real estate and the infrastructure that support the real estate). It has been taking place in periodicals and broadcast media such as The Atlantic Monthly, The New York Times, The Wall Street Journal, Business Week, Newsweek, CNN, ABC, NBC among many others. This debate has been fueled by rising gas prices, the sub-prime crisis, the credit crunch, climate change and many other factors. The debate has revolved around simplistic concepts such as "the death of the suburbs", "the return to the city" and "the decline of the suburban American Dream." These are simplistic because they reflect an early to mid-20th century, industrial economy concept of how we build the built environment, not the realities of 21st century, knowledge economy concepts. It is perpetuated by the U.S. Census Bureau which divides the world into "central city" and "suburbs" when they compile their information. But it also infects most people's thinking. In my book, The Option of Urbanism, Investing in a New American Dream, I use the phrases walkable urban and drivable sub-urban to describe the only two ways we can build the built environment. Walkable urban places are high density (FAR of at least 0.8 and generally much higher), mixed-use places that have many means by which to get to them (car, transit, biking, walking , etc.) but once you are there, it is walkable. That means that within walking distance (1500 to 3000 feet or 100 to 500 acres), one can get most every daily need by walking. Drivable sub-urban places are low density (FAR between 0.05 and 0.3), modular-use places that you can only get there and only get around by car. The key issue is that walkable urban places are both in the central city and in the suburbs, as the Census defines them. In addition, drivable sub-urban places are both in the central city and in the suburbs, as the Census defines them. In other words, the old terms and concepts of central city and suburbs are pretty worthless. It is my estimate that 70% of the pent up demand for walkable urbanism will take place in what the Census calls the suburbs so it is not "back to the city" or "death of the suburbs" issues. There are many situations when drivable sub-urban development should take place in the central city; office parks and big box retail with surface parking lots are and should be built in central cities to broaden their economic offerings. Let's get our terminology up-to-date. It gets real confusing otherwise. ——- Christopher B. Leinberger is a land use strategist, developer, teacher, consultant and author, helping to make progressive development profitable. He is currently a Visiting Fellow at the Brookings Institution in Washington, D.C. He is the author of The Option of Urbanism: Investing in a New American Dream from Island Press.