Maps and Mapmaking
Maps have been made for thousands of years as a means to convey information about the surface of the Earth. Some maps are highly complex, organized data sets that have been assembled by cartographers, mathematicians, or geographers who wish to illustrate the lay of the land. Maps are able to provide tremendous amounts of information on a two-dimensional surface.
The History of Mapmaking
The first attempt to establish a grid system on Earth was in 150 C.E. by the Greek astronomer Ptolemy. He established the concept of imaginary lines that intersected at regular intervals, making it possible to locate a particular position from reference points on a grid.
Using information from his astronomical predecessors, Ptolemy established latitude as imaginary parallel lines, equally spaced, that circled the world in a horizontal plane. The zero degree parallel was the equator. He chose this parallel as zero because it has the largest diameter of any latitude.
Ptolemy proposed the concept of longitude, equally spaced imaginary lines that run north and south, as a way of dividing Earth into a set of lines that are parallel to one another at the equator. The zero meridian was originally chosen arbitrarily by Ptolemy. Throughout the centuries, the Prime Meridian has been changed as a result of various political interests. Through an international consensus, it was agreed that the prime meridian would pass through Greenwich, England, going from the North to the South Poles.
Mathematics in Maps
One of the first mathematical calculations to be determined for a map is the scale. Because it is usually infeasible to make a life-sized map, mapmakers must reduce the size of real objects and distances proportionally. The smaller a map scale, the more detail the maker can include.
Projections are one of the most difficult tasks of mapmaking. A projection is an attempt to draw the gridlines of a spherical object on a flat surface. In reality, it is impossible to draw the true gridlines of Earth on a flat surface without losing some of the mathematical accuracy of distance or area. For example, on a flat map, Greenland appears much larger in proportion to areas that are closer to the equator than it is in reality.
Most projections are derived from geometric figures. To make geometric maps, trigonometry is used to solve the problems of distortion.
Gerardus Mercator was one of the first people to solve the problem of distortion in maps. In 1569 he drew his map so that the meridians remained vertical and equally spaced while the parallels increased in spacing as they approached the equator. Mercator determined the correct degree of increase between parallels from the secant of the latitude.
Cylindrical maps represent Earth as a cylinder on which the parallels are horizontal lines and the meridians are perfectly vertical. These maps may seem impractical because of the tremendous distortion in the polar latitudes, but they are excellent for use with compass bearing, which can be plotted as straight lines.
Conic projections are maps drawn as a projection from a point above the North or South Poles. The map intersects Earth at a point tangent to a specific point on the sphere, usually a pre-selected parallel. Polyconic projections are used in large-scale map series. Each conic section is made to correspond to a particular latitude.
Azimuthal projections are maps made from viewing Earth from a particular perspective; either outer space, the interior of Earth, or different
Geographers and cartographers continue to improve the accuracy of maps. Mapmaking has evolved from the beautifully handpainted paper maps of ancient times to the sophisticated Global Positioning System (GPS) of the twenty-first century, which provides accurate geographic details via satellites.hemispheres of Earth. The map itself is a flattened disk with its center at a point tangent to a reference point. The map represents a view from one of the specific points mentioned. These types of maps are most often seen as polar projections in which the polar land and sea are shown together as a circle.
Digital Maps
Maps are often updated using aerial photographs. These photographs are known as digital orthophoto quadrangles (DOQ). DOQs are altered so that they have the geometric properties of a map. There are four elements necessary in an aerial photograph: three identifiable ground positions, camera calibration specifications, a digital elevation model of the area in the photograph, and a high-resolution digital image of the photograph. The picture is then processed pixel by pixel to create an image with true geographic positions.
Geographers, mathematicians, and computer analysts, among others, continue to improve the quality and reliability of maps. Modern digital technology has helped enhance our current understanding of the surface of Earth. Mapmaking will continue to become more refined as technology continues to improve.
Cartographer; Geography; Global Positioning System.
Bibliography
Brown, Lloyd A. Map Making: The Art that Became a Science. Boston: Little, Brown, 1960.
Goss, John. The Mapping of North America: Three Centuries of Map-Making, 1500–1860. Secaucus, NY: Wellfleet Press, 1990.
Menno-Jan Kraak, and Allan Brown. Web Cartography: Developments and Prospects. New York: Taylor and Francis, 2000.
Robinson, Arthur, et al. Elements of Cartography, 6th ed. New York: John Wiley, 1995.
Internet Resources
Digital Backyard. USGS TerraServer. <http://mapping.usgs.gov/digital backyard/>.
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