Note that the data published in the 2002 State of the Nation’s Ecosystems Report as well as the 2003 and 2005 Web-Only Updates have been superseded by the 2008 Report and thus should be used with caution. For the most recent data, purchase the 2008 Report from Island Press.

The Indicator

The indicator reports the amount of publicly accessible open space per resident for major urban and suburban areas in the United States. “Natural” lands include areas managed for their natural values as well as areas that are vegetated, but also relatively highly managed, such as playing fields and parks. Minor amounts of pavement or other “hard” surfaces would not preclude an area from being considered “natural.”

According to the National Research Council (2000, p. 22), the natural environment provides people with a variety of ecological goods and services, including “recreation, aesthetic enjoyment, and spiritual experience.” This indicator is an important measure of the capacity of urban and suburban areas to provide recreational and aesthetic enjoyment in an unbuilt environment close to home.

Definitions: “Open space” means unbuilt land or water areas dominated by naturally pervious surfaces. A grassy park or golf course would qualify as open space; a paved playground would not. A river or lake would qualify as open space, as would some cemeteries. Satellite imagery will soon provide 5-meter resolution images, but whether there should be a minimum size to qualify for inclusion––that is, whether open space or parkland loses recreational or aesthetic utility below a threshold parcel size––is a question yet to be answered.

“Publicly accessible” means publicly or privately owned open space to which the general public has legal access, with or without an entry fee. A space is not publicly accessible if access is limited to members of specific groups or organizations. For example, a public or private golf course would be considered publicly accessible unless entry was restricted to club members. A farm would not be publicly accessible, nor would a country club. A privately owned but vacant and overgrown industrial site would not be publicly accessible.

The Data Gap

There are at least two methods for calculating the amount of open space and determining whether it is publicly accessible:

Self-Reported Acreage: Cities, counties, special districts, and states can report the acreage of public parks and open spaces they administer inside metropolitan areas. Public parks and publicly owned open spaces would be assumed to be publicly accessible. Accuracy would be limited by inconsistent standards among jurisdictions in the same metropolitan area for defining parks and open spaces. Historical data from cities may be affected by boundary changes associated with annexations. Hardened playground surfaces would likely be included in the data; many water bodies would likely be excluded, as would private lands that are effectively public by virtue of the owners’ access policies. Direct Measurement: Satellite imagery can identify unbuilt open spaces with naturally pervious surfaces. Tax assessment records might be used to locate tax-exempt parcels inside the identified open spaces. The tax records normally identify the basis for each parcel’s tax exemption, making it possible to infer which parcels are publicly accessible. More research is needed to determine the suitability of tax assessor records. Although tax assessment records are usually maintained by counties, in some jurisdictions cities, districts, or states may maintain the records. Some assessment records are maintained by these local jurisdictions in geographic information system (GIS) databases. GIS-based records make it easier, faster, and cheaper to derive the indicator, although it would be possible to do it with non-GIS records.

The data from both methods can be aggregated within each metropolitan area and aggregated again across all metropolitan areas for a national measure.

Before such an effort is put in place, some threshold of extent or population size would have to be developed to determine which cities, suburbs, and aggregations of the two should be included. Once this selection is completed, the per capita calculations would be carried out using population data from the Census Bureau.

References

National Research Council. 2000. Ecological indicators for the nation. Washington, DC: National Academy Press.