OCEANOGRAPHY: Mapmaking: Redrawing the Boundaries

▪ 1995

      Once considered a form of art, cartography is no longer limited to features of the Earth's surface drawn by hand on paper. Today mapmaking is being revolutionized by technologies that are advancing it into the Information Age, where the explosion of data and changing needs of scientists, policy makers, and commercial enterprise are remaking ideas of what maps are and what they can show. Three of the technologies that are transforming traditional cartography are geographic information systems (GIS), the Global Positioning System (GPS), and high-resolution satellite imagery.

      GIS comprise software and hardware systems that relate and display collected data in terms of geographic, or spatial, location. The ability of GIS quickly to overlay new information on top of existing base data and to display it in colour on a computer screen is helping users conduct analyses and make decisions related to geology, ecology, land use, demographics, transportation, and other domains in ways never before possible. For example, in searching for a safe site for a landfill, a researcher may direct the computer to overlay a regional elevation map with data on various types of soil. The soils data, in turn, can be removed or overlaid still further, say, with data on underground water.

      Complementing GIS is GPS, a technology funded by the U.S. Department of Defense. Conceived for such applications as warship and aircraft navigation and missile guidance, GPS has become the foundation of modern mapmaking. GPS consists of a fleet of 24 satellites that transmit signals globally around the clock. In conjunction with receivers on Earth, GPS can quickly and accurately determine the latitude, longitude, and altitude of a point on or above the Earth's surface. A single GPS receiver costing as little as $250 can find its own position in seconds from GPS satellite signals with an accuracy of 50 m (165 ft). Accuracies of less than 10 cm (4 in) are possible if two (more expensive) receivers are used together. This capability has reduced the cost of acquiring the spatial data needed for making maps while increasing cartographic accuracy.

      For decades the U.S. and the former Soviet Union have used high-resolution satellite imagery for military purposes. Only recently, however, has the civilian community in the U.S. been given permission to launch satellites that can resolve objects on the ground as little as a metre apart. Existing civilian satellites can obtain a 10-m (33-ft) ground resolution, and data from those satellites already have had an enormous impact on mapping, allowing the creation of specialized maps that can be used, for example, to predict crop yields, model optimal lumber harvests, or chart ever changing wetlands. With the higher resolution imagery expected to be available in 1995, along with GPS-controlled satellite positioning, mapmaking is certain to redraw its conceptual borders even more.

      (JOHN D. BOSSLER)

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