Map

A

Observation

The basis of a modern map is a careful survey giving geographical locations and relations of a large number of points in the area being mapped. Today, nearly all original maps make use of aerial photographs in addition to traditional land-surveying information (see Aerial Survey; Surveying). Satellite photographs can furnish a wealth of accurate information about various features on the earth's surface, including the location of mineral deposits, the extent of urban sprawl, vegetation infestations, and soil types.

B

Compilation and Reproduction

Once the data have been collected, the map must be carefully planned with regard to its final use so that all relevant information can be rendered clearly and accurately. The collected surveys and photographs are then used to enter a large number of points on a grid of crossed lines corresponding to the projection chosen for the map. Elevations are determined and contour lines, if used, are drawn directly from stereoscopic pairs of photographs by using very complex instruments such as the multiplex. The courses of roads and rivers and the positions of other features are drawn in the same way. Final preparation of a map for printing begins by making a series of sheets, one for each color used on the map. These sheets are made of an opaque coated plastic; lines and symbols are scribed onto the surface by a sharp etching tool that removes the opaque coating. Each such sheet is a negative from which a lithographic plate is made. See Lithography.

Another type of map is an orthophotomap, in which actual photographs form the body of the map. Such a map is a mosaic of carefully pieced portions of aerial photographs, which have been changed by the use of an orthophotoscope to eliminate scale and angle distortion. During the 1970s advancements were made in computer-generated maps. Data can be stored on the coordinates of a geographic area and on the distribution of statistical phenomena in the area. A device such as a continuous-curve plotter enables a computer to draw accurate maps from the stored data. Computer-generated maps can also be displayed on a video screen, where an operator can easily make alterations in the content. Because such maps, and each incorporated change, can be stored in the computer, they are useful in furnishing an animated picture of a change over a period of time.

VI

History of Maps

The earliest existing maps were made by the Babylonians about 2300 bc. Cut on clay tiles, they consisted largely of land surveys made for the purposes of taxation. More extensive regional maps, drawn on silk and dating from the 2nd century bc, have been found in China. The ability and need to make maps would appear to be universal. One of the most interesting types of primitive map is the cane chart constructed by the Marshall Islanders in the South Pacific Ocean. This chart is made of a gridwork of cane fibers arranged to show the location of islands. The art of mapmaking was advanced in both the Maya and Inca civilizations, and the Inca as early as the 12th century ad made maps of the lands they conquered.

---

---

The first map to represent the known world is believed to have been made in the 6th century bc by the Greek philosopher Anaximander. It was circular in form and showed the known lands of the world grouped around the Aegean Sea at the center and surrounded by the ocean. One of the most famous maps of classical times was drawn by the Greek geographer Eratosthenes about 200 bc. It represented the known world from England on the northwest to the mouth of the Ganges River on the east and to Libya on the south. This map was the first to be supplied with transverse parallel lines to show equal latitudes. The map also had some meridians of longitude but they were irregularly spaced. About ad 150 the Alexandrian scholar Ptolemy published his geography containing maps of the world. These were the earliest maps to use a mathematically accurate form of conic projection, although they incorporated many errors, such as the excessive extent of the Eurasian landmass. Following the fall of the Roman Empire, European mapmaking all but ceased; such maps as were made were usually drawn by monks, who often portrayed the earth inaccurately. Arabian seamen, however, made and used highly accurate charts during this same period. The Arabian geographer al-Idrisi made a map of the world in 1154. Beginning approximately in the 13th century, Mediterranean navigators prepared accurate charts of that sea, usually without meridians or parallels but provided with lines to show the bearings between important ports. These maps are usually called portolano or portolan charts. In the 15th century, editions of Ptolemy's maps were printed in Europe; for the next several hundred years these maps exerted great influence on European cartographers.

A map produced in 1507 by Martin Waldseemüller, a German cartographer, probably was the first to apply the name America to the newly discovered transatlantic lands. The map, printed in 12 separate sheets, was also the first to clearly separate North and South America from Asia. In 1570 Abraham Ortelius, a Flemish mapmaker, published the first modern atlas, Orbis Terrarum. It contained 70 maps. During the 16th century many other cartographers produced maps that incorporated the ever-increasing information brought back by navigators and explorers. It is Gerardus Mercator, however, who stands as the greatest cartographer of the age of discovery; the projection he devised for his world map proved invaluable to all future navigators.

The accuracy of later maps was greatly increased by more precise determinations of latitude and longitude and of the size and shape of the earth. The first maps to show compass variation were produced in the first half of the 17th century, and the first charts to show ocean currents were made about 1665. By the 18th century, the scientific principles of mapmaking were well established and the most notable inaccuracies in maps involved unexplored parts of the world.

By the late 18th century, as the initial force of world exploration subsided and as nationalism began to develop as a potent force, a number of European countries began to undertake detailed national topographic surveys. The complete topographic survey of France was issued in 1793; roughly square, it measured about 11 m (about 36 ft) on each side. Britain, Spain, Austria, Switzerland, and other countries followed suit. In the United States the Geological Survey was organized in 1879 for the purpose of making large-scale topographic maps of the entire country. In 1891 the International Geographical Congress proposed the mapping of the entire world on a scale of 1:1,000,000, a task that still remains to be completed. During the 20th century, mapmaking underwent a series of major technical innovations. Aerial photography was developed during World War I and used extensively during World War II in the making of maps. Beginning in 1966 with the launching of the satellite Pageos, and continuing in the 1970s with the three Landsat satellites, the U.S. has been engaged in a complete geodetic survey of the surface of the earth by means of high-resolution photographic equipment. In spite of the great advancements in cartographic technique and knowledge, substantial portions of the earth's surface have not been surveyed in detail. Surveying work continues, for instance, on the continent of Antarctica.

	More from Encarta
	•  Important Notice: MSN Encarta to be discontinued. Learn more. •  Presidential Myths Quiz •  Coffee break: Recharge your brain