Open Space Data

Two federal agencies provide useful data on urbanization and rural open space. The Natural Resources Conservation Service does a natural resource inventory every five years, and this inventory estimates the amount of urban and rural development. The decennial census measures the land area of every census tract and classifies census tracts in such categories as urban area, urban cluster, and place. Both of these data sources agree that more than 95 percent of the United States remains rural open space.

The census and the Natural Resources Inventory measure different things, so naturally the numbers are a little different. Census data include the number of square miles in urbanized areas of 50,000 people or more, urban clusters of 2,500 people or more, and places, which include all incorporated towns of any size as well as any unincorporated concentration of people deemed by the Census Bureau to be recognized as a place.

Some of the small towns in the census have so few people that they may as well be open space. Forty-five towns occupying nearly 700 square miles have a population of zero. Another sixty towns covering 2,100 square miles each have less than ten people. Nearly 1,600 towns with populations of 10 to 99 together cover well over 25,000 square miles. This means the average density of towns smaller than a hundred people is less than four people per square mile. The average density of all non-urban places is less than 200 people per square mile. Since the average density of urban areas is 2,600 per square mile, and urban clusters is nearly 1,500 per square mile, the Census Bureau has obviously included large areas of open space in its non-urban places.

The problem is that the Census Bureau seems to count all the land in a town’s legal boundaries, and that sometimes includes a lot of land. Towns or boroughs in Alaska can occupy hundreds of square miles yet contain only a handful of residents. In short, the Census Bureau’s definition of “places” exaggerates the area of developed land, and the true extent of urbanized land is somewhere between the area of urbanized areas/urban clusters and the area for places.

The Natural Resources Inventory (NRI) was designed to measure the extent of farms and forests, and developed areas are only an afterthought. Unlike the census, which is an exact measurement, the NRI is a sample, so its accuracy is not as high. The NRI also does not include Alaska, but such a tiny portion of Alaska has been developed that this is not a serious problem.

For each state, the NRI estimates the amount of land in large urban developments, meaning larger than 10 acres. Parks and other open spaces smaller than 10 acres are counted in large urban developments if they are completely surrounded by other developed land. The NRI also estimates the extent of small built-up areas, meaning between a quarter acre and 10 acres. Such small built-up areas probably includes such rural developments as grain elevators or agricultural processing facilities. The NRI also estimates the amount of rural land used for transportation, including roads and railroads.

The table below shows the results of the two measurements for the U.S. as a whole. The NRI says 3.1 percent of the U.S. is urbanized and 1.2 percent is in rural developments and transportation. The census says that 2.6 percent is in urban areas of 2,500 people or more and another 2.8 percent is in small towns and places. Considering the exaggerated extent of small towns in the census, it is clear that well under 5 percent of the U.S. has been developed.

Census and NRI Estimates of Developed Land
                          Land Area      Percent
                         Square Miles    of Total
2000 Census
Urban areas                  71,961         2.0
Urban areas & clusters       92,508         2.6
All places                  189,374         5.4
1997 Natural Resources Inventory
Large urban                 109,326         3.1
Large & small built up      118,875         3.4
Developed                   152,726         4.3
Total U.S. Land           3,537,438       100.0

The following table has a breakdown by state of the percent of urbanized land (urban areas plus urban clusters) and places, and the NRI urban land (both large and small) and developed land (both urban and rural). The only states that are more than 20 percent developed are the tiny states, such as Massachusetts and Maryland, on the east coast. With the exception of Ohio, other states that are more than 10 percent developed are also on the Atlantic seaboard.

You can download more detailed files of census and Natural Resources Inventory data. The numbers in the NRI file are in thousands of acres, while the numbers in the Census are in square miles. To convert, remember that there are 640 acres in a square mile.

Census and Natural Resource Inventory Measurements of Urban and Developed Lands
                                    2000 Census        1997 Nat. Res. Inv.
                   Land Area     Percent    Percent    Percent     Percent
                  Square Miles    Urban      Places     Urban     Developed
Alabama               50,744        3.5        9.7        5.5        7.2
Alaska               571,951        0.0        4.7        0.0        0.0
Arizona              113,635        1.5        5.4        1.7        2.3
Arkansas              52,068        1.7        4.6        2.9        4.4
California           155,959        5.1        8.6        4.9        5.6
Colorado             103,718        1.2        2.6        1.8        2.6
Connecticut            4,845       36.3       39.8       25.8       28.1
Delaware               1,954       15.5       17.8       13.9       15.5
District of Columbia      61       99.8      100.0      100.0      100.0
Florida               53,927       11.4       16.2       13.0       14.5
Georgia               57,906        6.4        9.6        9.4       11.2
Hawaii                 6,423        5.5       17.5        3.8        4.5
Idaho                 82,747        0.5        0.8        0.8        1.5
Illinois              55,584        6.4        8.7        7.1        9.0
Indiana               35,867        6.2        8.2        8.0       10.2
Iowa                  55,869        1.5        3.7        2.3        5.0
Kansas                81,815        1.1        1.8        2.0        5.5
Kentucky              39,728        3.1        5.2        5.5        7.6
Louisiana             43,562        3.8        6.9        4.3        5.4
Maine                 30,862        1.2        4.2        2.8        3.6
Maryland               9,774       18.4       23.3       15.1       16.4
Massachusetts          7,840       35.8       40.5       27.4       29.0
Michigan              56,804        5.9        7.3        9.0       10.1
Minnesota             79,610        1.9        5.2        2.8        4.4
Mississippi           46,907        2.0        4.7        3.6        5.4
Missouri              68,886        2.6        4.7        3.9        5.9
Montana              145,552        0.2        2.0        0.4        0.9
Nebraska              76,872        0.6        1.0        1.1        2.6
Nevada               109,826        0.5        2.8        0.5        0.6
New Hampshire          8,968        6.2       10.3        9.2       10.8
New Jersey             7,417       37.6       44.1       34.6       35.4
New Mexico           121,356        0.6        1.7        1.0        1.7
New York              47,214        8.3       10.8        9.3       10.8
North Carolina        48,711        7.3       10.3       10.5       12.4
North Dakota          68,976        0.2        0.9        0.6        2.5
Ohio                  40,948        9.8       12.6       13.0       14.4
Oklahoma              68,667        1.7        6.8        2.9        4.5
Oregon                95,997        1.1        1.5        1.4        2.1
Pennsylvania          44,817        9.5       12.4       13.5       15.0
Rhode Island           1,045       37.2       39.6       23.0       25.2
South Carolina        30,109        6.2        9.2        9.4       11.7
South Dakota          75,885        0.2        0.9        0.7        2.1
Tennessee             41,217        5.9       10.6        8.1        9.7
Texas                261,797        2.7        5.0        4.2        5.3
Utah                  82,144        0.8        2.8        0.9        1.4
Vermont                9,250        1.6        2.9        3.9        5.6
Virginia              39,594        6.0        9.8        8.5       10.4
Washington            66,544        3.2        5.2        3.8        5.0
West Virginia         24,078        2.3        4.1        4.8        6.4
Wisconsin             54,310        3.0        5.6        5.1        7.1
Wyoming               97,100        0.2        1.9        0.4        1.1
Total              3,537,438        2.6        5.4        3.5        4.5
Census "urban" includes land in urbanized areas of 2,500 people or more.
Census "places" includes urban plus smaller towns and concentrations of people.
NRI "urban" includes urban developments of 10 acres or more.
NRI "developed" includes roads & rural developments of a quarter acre or more.