Because its surface is nearly spherical, the Earth is most accurately represented by a \Tglobe\t. However, a map, a flat image of the Earth, is more practical to use, more portable, and less costly to produce. It enables the user to see a generally complete representation of the world at one time. Mapmaking, or cartography, attempts to reproduce the Earth, or a portion of it, with a minimum of distortion so that the information contained in the map will be as accurate as possible. HISTORY OF MAPMAKING The first known map, a small clay tablet portraying an estate, was made late in the 3d millennium BC by the Sumerians. Early maps outlined real estate plots or prescribed construction specifications. About the 14th century BC, Egyptians made maps showing boundaries of property for use in taxation. Such maps were necessitated by the annual flooding of the Nile River, which obliterated property markers. The earliest important phase in the development of cartography can be traced to the ancient Greeks, who in turn are believed to have borrowed from the earlier cultures of the Middle East. Three major phases of mapmaking preceded the modern period: the Greek and Roman period, the Middle Ages, and the Renaissance. The Greek and Roman Period As early as the 8th century BC, the Greeks had already established a reputation as accomplished sailors and colonizers. By the early 6th century BC, Greece had become the leading center of geographical knowledge because of its many military and sailing expeditions. The first book on geography, describing a circular, flat Earth surrounded by ocean waters, appeared at the end of the 6th century BC. In the 3d century BC the famous scholar and mathematician \TEratosthenes of Cyrene\t calculated the Earth's circumference with remarkable accuracy. He and his contemporary \THipparchus\t laid the foundations for scientific cartography, developing a system of \Tlatitude\t and \Tlongitude\t. Much of what is known about ancient Greek cartography comes from the writings of \TStrabo\t and \TPtolemy\t. The latter produced a mapping textbook, Geographia, which included map projections and coordinates for places in the known world. The Romans, inheritors of the Greek knowledge of geography, surveyed their empire, indicating provincial boundaries and the location of towns, rivers, and roads. The Middle Ages During the Middle Ages, from approximately the 5th to the 15th centuries, little was added to scientific geographical knowledge and mapmaking. Cartographers during those centuries relied heavily on classical references and religious scripture for information and showed the Earth as a flat disk. The mappae mundi, derived from a 1st-century BC map, was a commonly used style, depicting a flat Earth with Jerusalem at the center, Asia at the top, Europe to the lower left, and Africa in the lower right corner. An ocean surrounded the clustered landmasses. Portolan or sea charts were introduced in the 13th century. These accurate renderings showed detailed shorelines and were used for navigation, primarily in the Mediterranean, into the 17th century. The Renaissance Between the 15th and the 17th centuries, great advances in cartography were related to important discoveries by explorers such as John \TCabot\t, Christopher \TColumbus\t, and Ferdinand \TMagellan\t. The invention of the printing press and the perfection of copper-plate engraving provided for the distribution of less expensive maps rendered in fine detail. The earliest map showing the New World was drawn in 1500 by the Spanish explorer Juan de la \TCosa\t. In 1507, Martin Waldseemuller prepared the first map on which the name America appeared, referring to the South American continent. By the middle of the 16th century, Europe had several major centers of cartographic activity. Italy was the principal mapmaking center. The Netherlands achieved superiority about 1570 and retained it through most of the 17th century, producing maps of great decorative beauty. Gerardus \TMercator\t founded a mapmaking house, and Abraham \TOrtelius\t published the first modern atlas in 1570. The Modern Period The first national survey was begun in France by the \TCassini\t family in 1733, establishing mapping as a government-sponsored pursuit. Such surveys included both topographic maps and marine charts. When lands in the United States west of Pennsylvania were opened for settlement, surveyors were faced with the problem of delimiting land parcels on a terrain with no features such as hills and trees. A system of townships and ranges was established, and evidence of this system remains in the rectangular road pattern common in areas west of the Appalachians. In 1879 the U.S. Geological Survey began a national mapping program that continues today. The current National Mapping Program is designed to provide accurate and up-to-date map data for the United States. The U.S. Geological Survey produces more than 10,000 different maps annually, many the result of advanced techniques. International cooperation in mapping resulted in the International Map of the World and the World Aeronautical Chart. Both have been rendered at a standard scale and show the entire world with standard symbolization. The International Map of the World was formulated in 1891, and the project was refined in 1909 and 1913; it remains to be completed. The World Aeronautical Chart, begun for strategic purposes during World War II, has been completed. MAP SCALE The scale of a map is the relationship between distance on the map and the corresponding distance on the Earth's surface. Large-scale maps show a small area and can contain much detail, whereas small-scale maps cover a large area. World maps are of necessity small scale, and a high degree of detail is impossible within the limits of the sheet size. A map of a city block, on the other hand, can be drawn to large scale with great detail. Scale can be expressed in one of three ways: fractionally, verbally, or graphically. A fractional scale gives the equivalence of one unit on the map to the number of units on the ground shown within that one map unit. The fractional scale "1:24,000" indicates that one unit on the map represents 24,000 comparable units on the ground. A verbal scale states the same relationship in words: "One inch on the map is equivalent to 0.38 miles on the ground." Common usage prescribes the placing of the map unit first and the ground units second. A graphic or bar scale is a line located in the legend that has been marked at intervals, much like a ruler. The ground distance between two points can be determined by measuring the distance between them on the map and then comparing that distance to the distance marked along the line or bar. Units are most commonly calibrated in round numbers, such as hundreds of kilometers or thousands of feet. TYPES OF MAPS It is theoretically possible to illustrate the geographic occurrence of virtually anything or any combination of things. This means that a theoretically infinite variety of map types exists. Most of the commonly used map types are either cultural or physical in nature, but some are both physical and cultural. Distributional Maps Distributional, thematic, or statistical maps depict the spatial variation of any phenomenon on the Earth's surface. With symbolization a map can show, for example, the occurrence of mineral deposits, animal species, or public libraries. Some maps are drawn with isolines connecting points of equal value. In maps showing elevations, the isolines are called contour lines. If a map contains isolines, the legend gives the interval at which the isolines are drawn, such as every 10 meters of altitude or each 5 degrees of temperature. Some maps use bands of color to indicate different intervals of value. While isolines assume a gradual change from one value to another, choropleths do not attempt to relate the value in one area to that of adjoining areas. Statistical data are often mapped using choropleths. The information to be shown is grouped by value, and each group is assigned a color or pattern. Those areas on the map with a given value are then overlain with the corresponding color or pattern. Geologic Maps The areal distribution of any of several geologic subjects is the concern of geologic maps. Bedrock maps show the geologic formation that is either exposed at the surface or overlain by surface deposits. Such maps are essential for construction projects and mineral exploration. Surficial geology maps contain data on sediment distribution. They often include information on the geologic time interval during which sediments were deposited. Tectonic maps display the actual or projected surface resulting from such structural elements as fault planes and fold axes. The degree to which initially horizontal rock layers have been deformed is also illustrated. Paleogeologic maps, including paleolithic and paleotectonic maps, show the areal geology present at some previous time. They can also show how the shape and size of continents and oceans have changed over time. Structure contour maps indicate the elevations or depths of formations relative to a continuous surface, such as the contact between two sedimentary rock formations. Isopach maps record the thickness of a specific stratigraphic interval (such as a layer of oil shale) by using isopachs--thickness contours. Lithofacies maps show rock types in a stratigraphic unit. A lithofacies map, for example, could show the location of sandstone in a formation of several different strata. Soil Maps Soil types present within a map area can be shown using one of several classification systems. Such maps are useful in making land-use decisions. Land-Use Maps The variation in activities within a given area is shown on land-use maps. Residential, industrial, and agricultural areas can be differentiated to provide information useful to city planners and road builders. Local governments use such maps in establishing zoning regulations. Economic Maps The geographic distribution of specific economic activities such as mining, manufacturing, and agriculture is found on economic maps. Rational location decisions for economic pursuits can be made by using economic maps. Zoological and Botanical Maps The area distributions of animals and plants are shown on zoological maps and botanical maps. Animal migration routes can also be illustrated, as well as the ecological status of an area. Such maps are useful to lumber companies and wildlife management personnel. Statistical Maps Quantitative information--that which may be measured--can be found on statistical maps. Patterns in the spatial variation of any given subject become evident when mapped, using symbols, bar or pie graphs, or isolines. Political Maps The boundaries of governmental units are found on political maps. Frequently political entities within boundaries are located and named. Choropleths are commonly used on these maps. Topographic Maps The visible shape of such landforms as visible mountains and valleys is shown on topographic maps. These can be used by engineers during the planning stages of construction projects. Topographic maps show the exact "lay of the land." Components of these maps include bench marks--points of known elevation relative to mean sea level, and contour lines connecting points of equal elevation. Most topographic maps produced by the U.S. Geological Survey are drawn to standard scales of 1:24,000, 1:62,500, or 1:250,000. The first of these is also known as the 71/2-minute sheet, the second, the 15-minute sheet--a reference to the latitudinal extent covered on the map. Orthophotoquads, another type of topographic map, are derived from aerial photographs or other remote sensors. They show a high degree of detail unobtainable by ground surveys. Bathymetric maps show marine topography by using contour lines drawn along intervals below sea level. Bathymetric charts aid in navigation. Cadastral Maps Cadastral maps identify parcels of land for purposes of ownership and taxation. Since a high degree of accuracy is important, most cadastral maps can be legally produced only by a duly authorized surveyor. Meteorological Maps The relationship between the atmosphere and weather conditions is shown on meteorological maps. Principal components include isobars, or lines of equal barometric pressure, and \Lisotherm\ls, lines of equal temperature. Wind speeds and directions are symbolized by a \Twind rose diagram\t. Satellite imagery has enabled meteorologists to improve the accuracy of such maps. Photographs taken from high-altitude satellites and transmitted to Earth show frontal activity and impending storms, thus enabling forecasters to predict weather further into the future than was possible with lower-altitude weather balloons. Transportation Maps One of the most frequently used map types is the transportation map. Highways, railroads, and airports are shown along with cities and points of interest. Historical Maps Exploration or trade routes, military movements, and former political units can be found on historical maps. Maps drawn at some earlier time, although not often very accurate, can be carefully interpreted by historians and used as a basis for drafting precise historical maps. MAP PROJECTIONS The Earth's shape is best represented by a sphere slightly flattened at top and bottom. Mapmakers, however, assume the Earth to be a perfect sphere. When transferring points from the curved Earth to the flat map surface, both equality in size and true directional relationship are impossible: the curved Earth's image suffers distortion. A cartographer must therefore select the map projection best suited to the eventual use of the map. Projections can be placed in one of three general groups, based on the method in which the information on the round Earth is transferred to the flat map--azimuthal, conic, or cylindrical. Reviewed by Walter W. Ristow Bibliography: Bagrow, Leo, History of Cartography, trans. by D.L. Paisley, revised and enlarged by R.A. Skelton (1964; repr. 1985); Birch, T.W., Maps, Topographical and Statistical, 2d ed. (1964); Bricker, Charles, and Tooley, R. V., A History of Cartography: 2,500 Years of Maps and Mapmakers (1969); Campbell, J., Introductory Cartography (1984); Crone, G.R., Maps and Their Makers, 5th ed. (1978); Greenhood, David, Mapping, rev. ed. (1964); Harley, J.B., and Woodward, D., eds., The History of Cartography (1987); Lawrence, G.R.P., Cartographic Methods (1971); Monmonier, Mark, How to Lie with Maps (1991); Ristow, Walter W., Guide to the History of Cartography (1973); Robinson, Arthur H., Sale, Randall D., and Morrison, Joel, Elements of Cartography, 5th ed. (1984); Robinson, Arthur H., and Petchenik, Barbara, The Nature of Maps: Essays Toward Understanding Maps and Mapping (1976); Skelton, Raleigh A., Maps: A Historical Survey of Their Study and Collecting, ed. by David Woodward (1972); Speak, P., and Carter, A.H., Map Reading and Interpretation, 4th ed. (1974); Steers, James A., Introduction to the Study of Map Projections, 15th ed. (1970); Thrower, Norman J., Maps and Man: An Examination of Cartography in Relation to Culture and Civilization (1972); Tooley, Ronald V., Tooley's Handbook for Map Collectors (1985); Wilford, J.N., The Mapmakers (1981); Woodward, David, ed., Five Centuries of Map Printing (1975). See also: \Tsurveying\t.