Scientists are using a major advance in satellite-based land surface mapping to create
more accurate and detailed maps of our cities. These maps provide urban planners with a better understanding of city growth and
how rainfall runoff over paved surfaces impact regional water quality.
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.
Andrew Smith, a faculty research assistant at the Mid-Atlantic Regional
Earth Science Applications Center produced a map of the
Washington-Baltimore area that quantifies how much impervious surface
there is across the entire region. 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 District of Columbia and surrounding watersheds in Virginia and
Maryland have levels of impervious surfaces between 20 percent and 30
percent percent. Areas between and beyond the Baltimore-Washington
corridor are more "green" with levels that range from 0 percent to 20
percent impervious surface areas.
The image above shows the extent of impervious surfaces in and around
Washington and Baltimore. Red represents high concentrations of
impervious surfaces. Blue represents moderate concentrations and green
represents low concentrations of impervious surfaces. The base image was
acquired by NASA's Landsat satellite, while the map of impervious surfaces
was derived with data from both Landsat and Space Imaging's
high-resolution IKONOS satellite.