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'Green, More or Less' Methodology

By Washington Post Staff

No single agency keeps tabs on the loss of green space in the Washington region, so The Washington Post turned for that expertise to the National Center for Resource Innovations in Rosslyn, a private, nonprofit educational organization funded by Congress to supply geographic information to policymakers.

Using data from the U.S. Census, Metropolitan Washington Council of Governments, state and county governments and aerial pictures, center officials estimated how many acres of green space have been converted to development in the Washington area between 1980 and 1990. Green space is forest, farmland, wetlands and "barren" land that has been cleared but is not currently in use.

They also projected how many acres are expected to be converted for development during the next 20 years. To get that figure, center officials took each county's estimates of where people are expected to live by 2020, and where counties are planning commercial and industrial growth. If an area is projected to have at least one housing unit per 10 acres in the year 2020, center statisticians classified it as developed and the land appears shaded on the 2020 map. Though most suburban residents don't live on 10 acres, the standard was chosen because it usually means that at that density, the land no longer is a forest or profitable farm.

Shaded areas don't necessarily mean that section of a county is completely paved over. In some counties, substantial open space still exists within areas that are considered developed.

Each county reviewed the completed maps. The maps and charts are projections because no one can fully predict what will happen in the next two decades due to changes in market conditions and local government land use policies.

© 1996 The Washington Post Company

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