Some Numbers on Open Space

• 1990 Census Bureau estimates of the size of some 400 major metropolitan areas, which conclude that about 1.7 percent of the U.S. has been "urbanized" in a metro area of 50,000 people or more;
• Federal Highway Administration annual updates to the Census Bureau estimates, the latest of which, for 1997, more than doubles the 1990 urbanized area to 3.6 percent; and
• The Natural Resources Conservation Service's semi-decennial inventory of farm lands, the 1992 edition of which indicates that 4.0 percent of the U.S. has been "developed," including both urban developments and rural roads and railroads.

The Federal Highway Administration annual updates are performed largely by state transportation officials who clearly use different criteria from the Census Bureau and who may be seeking to inflate urban sizes in order to justify larger federal transportation grants.

The Natural Resources Inventory data focus on farmlands but count forests, water, pasture, and "developed" lands, including rural roads and railroads. But the inventory is based on a sample whose reliability is low for smaller breakouts -- and the developed lands are one of the smallest breakouts. Also, the Natural Resources Inventory does not include Alaska, though this should not be a problem since a tiny proportion of that state has been developed.

The 1997 Natural Resources Inventory data were not yet available when this was written. For an analysis of those data, see Sprawl and the 1997 Natural Resources Inventory.

A third source of data consists of the 23,435 "places" identified by the Census Bureau for the 1990 census. A "place" is a city, town, village, or unincorporated concentration of population identified by the bureau. These places range from New York City (population 7.3 million) to four incorporated towns whose 1990 population was zero.

As noted in Some Numbers on Density, data for all 23,435 places may be downloaded from the Census Bureau web site. They must be downloaded separately for each state and the process is somewhat tedious. A zipped file containing all these data is 944KB; if there is enough demand, I will post it on the web.

The 1990 census estimate of the total land area occupied by all 23,435 places was 126,141 square miles, which is about 3.5 percent of the U.S. as a whole. Assuming that another half a percent is covered by rural roads and railroads, this tallies well with the Natural Resources Inventory.

Still, it is debatable whether some of the places identified by the Census Bureau ought to be counted as developed. Most people would say that farm land is all "open space," even including the farm house, barn, and other outbuildings. A close scrutiny of the Census Bureau data suggests that some of the places identified by census takers are really mostly open space.

For example:

• Bay Lake, Florida, covers 18.6 square miles but has a population of zero.
• Valley Park, Oklahoma, covers 1.1 square miles and has a population of one.
• Sitka, Alaska, has a population of 8,900 people but supposedly covers nearly 2,900 square miles, for a density of just 3 people per square mile.
• Willow Creek, California, has less than 1,600 people on more than 200 square miles, for a density of under 8 per square mile.
• Juneau, Alaska, has 26,000 people on 2,600 square miles, for a density of 10 people per square mile.

If we just count places whose densities are greater than 500 people per square mile, then only 78,000 square miles, or 2.2 percent of the nation, are developed. Even if we go down to 200 per square mile, less than 92,000 square miles, or 2.5 percent of the U.S., are developed.

On a state-by-state basis:

• 100 percent of DC is developed;
• About a quarter of New Jersey is developed;
• About a fifth of Massachusetts is developed;
• About 18 percent of Connecticut and Rhode Island are developed;
• About 16 percent of Hawaii and 15 percent of Maryland are developed.
• About 5 to 10 percent of California, Delaware, Florida, Illinois, Indiana, New York, Ohio, Pennsylvania, Tennessee, and Virginia are developed.
• Slightly more than 5 percent of Georgia and North Carolina are included in all places, but less than 5 percent are in places with densities over 200 per square mile.
• The other 32 states are all less than 5 percent developed.

The table below shows for each state:

• The total number of square miles in the state;
• The number of square miles of each state in 1990 Census Bureau urbanized areas;
• The number of square miles counted as developed by the 1992 Natural Resources Inventory;
• The number of square miles of each state in 1997 Federal Highway Administration urbanized areas;
• The number of square miles in 1990 places denser than 500 per square mile;
• The number of square miles in 1990 places denser than 200 per square mile;
• The number of square miles in all Census Bureau 1990 places.