Cartography Article - 2

The View from Above

Two centuries ago a pair of earthbound cartographers named Jacques and Cesar-Francois Cassini relied on what their eyes could see across the curving surface of France to collect the most accurate survey measurements of a nation up to that time. A century ago mapmakers ascended in balloons to record bird's-eye views of the land with a new invention-the camera.. Forty years ago as airplanes, then rockets, lifted human vision higher and higher, the U.S. Navy coined the term "remote sensing" examining Earth from a distance.

High-altitude photographs and satellite images give cartographers views of a world they have never seen in its entirety. Digital images, many at wavelengths invisible to humans, instantly provide information that would once have taken lifetimes to collect, if it could have been gathered at all. For the first time cartographers can "see" through desert sands and polar ice. They can map the hole in the ozone layer and the health of trees in a rain forest. They can look through night and clouds using radar or create mosaics of the globe by piecing together satellite and sonar images to produce the views of land and ocean tloor below.

Computer-based geographic information systems (CTIS) let cartographers manipulate such data, layering information to create maps that answer questions in visual terms and illustrate hidden relationships between geographic phenomena. With such knowledge comes power - power to exploit or conserve resources and to detect environmental threats long before they become apparent on Farth. Eyes in the Sky Distant geostationary satellites orbit 22,300 miles up, rotating with Earth for a constant view. Low-altitude satellites pass over the Equator and polar regions many times a day, eventually viewing most of the planet turning below.

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