To hear the critics of urban sprawl tell it, every new housing development means we're "running out of farmland." Every new strip mall puts us one step closer to "the paving of America." The danger occurs when these clichés become the basis of public policy.

Sound thinking about land use requires putting sprawl in its proper perspective. Start with a simple fact: All development, including roads, highways and military bases, as well as urban and suburban housing and commercial buildings, consumes only about 5 percent of the total land area of the continental United States. This is only about half as much as European nations, all of which have thriving agriculture and ample open space. Even the Clinton administration has concluded that "loss of farmland poses no threat to U.S. food and fiber production."

The rate at which land is being used each year is hard to pinpoint because up-to-date and comprehensive national data are unavailable. The U.S. Geological Survey estimated in the 1980s that since the end of World War II, the annual rate of land development has been about 1.3 million acres a year. This sounds huge, but it is only 0.07 percent of the 1.8 billion acres of land in the continental United States. At this rate, it would take nearly 15 years to develop just 1 percent of the nation's land area.

Recently, preliminary figures from the 1997 National Resources Inventory (NRI) upped the estimated rate of land development to 3 million acres a year. But the Department of Agriculture, which produces the NRI, has already withdrawn the estimates because of a "computer programming error," and will restate them next month. Some of the revisions, the Department of Agriculture has admitted, will be "substantial."

Of course, the controversy involves more than just the raw amount of land being used. Critics of sprawl think we are developing land at too low a density. They like to cite examples such as the Chicago metropolitan area, whose population grew by just 4 percent between 1970 and 1990 while the developed land area grew by 55 percent. St. Louis appears even more dramatic; regional population has grown by 17 percent since 1960, but the developed land area has grown by 125 percent.

These statistics are superficial, ignoring the fact that density should fall as household sizes shrink and affluence increases. In fact, density in the central cities has been gradually declining, and the suburbs expanding, for more than a century. In the 19th century, it was not atypical for U.S. cities to have densities of up to 100,000 people per square mile. Urban reformers of the time thought that cities were overcrowded, and that dispersing people to the suburbs was an improvement. The technology for lowering the density of crowded cities was, ironically, the same technology that supposedly will raise density today: rail transit.

What is happening is simple to understand: the suburban lifestyle that used to be only affordable to the rich and upper middle class is now within reach of the working class. (The fastest-growing demographic segment of suburban residents is minorities.) It is unrealistic to expect that urban densities will remain constant as the middle class grows more numerous and prosperous, or that Chicago's new suburbs will develop at the same density as the central city itself (12,000 people per square mile). As Gregg Easterbrook, senior editor of The New Republic, bluntly puts it, "Sprawl is caused by affluence and population growth, and which of these, exactly, do we propose to prohibit?"

The sprawl controversy is really about our collective unhappiness with the rapid changes that growth brings to our communities. This is a reasonable issue and a challenge for governance. But we aren't "running out of land," and policies that that seek to lock up land will only have the effect of keeping people from achieving their rightful share of the American Dream.

This essay by Steven Hayward, a senior fellow at the Pacific Research Institute in San Francisco, is adapted from his chapter in the new Heritage Foundation book, "A Guide To Smart Growth."