NASA’s Earth Observatory reports on a new satellite-imagery-based mapping — the example is of the Washington-Baltimore area — that shows how much “impervious surface” there is in the area: “These space-based maps of buildings and paved surfaces, such as roads and parking lots, which are impervious to water, can indicate where large amounts of storm water runs off. Concentrated runoff leads to erosion and elevated discharge of soil and chemicals into rivers, streams, and ground water. … Baltimore and the counties that border it have at least 20 percent, and up to 40 percent, impervious surface area, indicating that pollution from runoff could be a problem.”

The image here is false-colour (and frankly looks like Jackson Pollock had something to do with it); the linked page has high-resolution false-colour and true-colour versions available. Via BLDGBLOG.