Topics: Geomatics - Cartography
Cartography is the creation, production, and study of maps. Cartographers are often geographers who specialize in the combination of art, science, and technology to make and study maps. Some cartographers teach mapmaking skills and techniques, some design and produce maps, and some are curators of map libraries. All cartographers, however, focus on maps as the object of their study or livelihood. In other cases, biologists, economists, geologists, hydrologists, planners, and others can engage in cartography to summarize or analyze spatial data. Geologists, for example, produce highly specialized geologic maps to show the three-dimensional arrangement of rock types in an area.
A major change in cartography during the past decade has been the growing use of geographic information system (GIS) software to produce, store, and use maps. GIS software can be used to create custom maps that cover an area or portray features of specific interest to a user. For example, a map showing vegetation types can be placed over a shaded relief map of the earth's surface to illustrate the relationship between biology and topography. GIS software can also be linked to computer simulations of processes such as flooding or earthquake damage to help communities develop emergency response plans. Digital maps can also be widely distributed using internet map servers that allow users to interactively explore a large map by scrolling and zooming.
Showing three-dimensional relationships in two dimensions
When creating a flat map of a portion of the earth's surface, cartographers first locate their specific area of interest using latitude and longitude. They then use map projection techniques to represent the three-dimensional characteristics of that area in two dimensions. Finally, a grid, called a rectangular coordinate system, may be superimposed on the map, making it easier to use.
History of Cartography
History of Cartography, the history of cartography (map-making) and the study of how maps have influenced human affairs in the past. It describes not only the technical process used to make maps but also observes the motives for their making and their role in forming society’s views of space and place.
All humans possess a complex spatial knowledge of their environment. This “cognitive mapping” is created through direct experience and by communication with others. However, the more formal activity of map-making usually arises from the social needs of complex, extensive, and often highly bureaucratic societies.
For societies in which humans live and communicate within small groups, there is little need to make maps of the terrestrial environment. Thus, it is probable that the function of a few petroglyphs that can broadly be identified as maps from the Upper Palaeolithic period, c. 30,000 bc, was probably magical and cosmographical (perhaps associated with agricultural fertility rites), and most of the images are in abstract as if viewed from above. Important Neolithic examples include a representation of the Anatolian town Çatal Hüyük (in present-day Turkey) from about 6200 bc, and a series of complex topographical images from the foothills of the Italian Alps in Valcamonica dating from around 1500 bc.
II Map-Making in Local Traditional Societies
The very terms “map” and “cartography”, with their strong Western overtones, are unsatisfactory for small indigenous local cultures, even though iconic representations of territory that approach the European functions of maps have existed. The form of these spatial expressions may be in an oral or kinaesthetic ritual performance rather than an inscription industrial societies normally regard as a map.
There are several characteristics that indigenous maps share cross-culturally. One is to serve as a record of a creation story or genealogical lineage of a people, as in many Ojibwa migration charts. Here, where migrations, astronomical events, battles, and other events are recorded for posterity, the representation of time and space is conflated in the form of the map, so that events separated by many centuries may appear side by side. In Australia, reconstructions of the legendary tracks of ancestors, the Dreamings, are recorded in bark paintings and other media of Aboriginal art. Sacred and secular uses are often merged, so that a representation of the cardinal directions in the cosmos may be embodied in the plan of a village or house, as in the Dogon peoples of the Sahara.
There are also didactic or mnemonic uses. For example, the stick charts of the people of the Marshall Islands (the only group that made these forms of map) are a training aid for navigators for understanding the location and pattern of ocean swells. In Africa, memory boards are used in initiation rites establishing lineage of kingships and recalling the location of famous events. Among the Apache, notched sticks were used to remember landmarks for expeditions.
III The Classical Civilizations
A Mesopotamia and Egypt
Surviving artefacts from the civilizations of Mesopotamia show a profound knowledge of astronomy for astrological purposes, as well as a practical knowledge of geometry and surveying in field surveys for taxation and irrigation purposes. These are mainly in the form of hundreds of clay tablets recording cadastral (landownership) information, mostly dating from the 1st millennium bc. Fewer map artefacts survive from ancient Egypt, but there is graphic evidence in wall paintings, inscriptions, and manuscripts of surveying instruments used to survey buildings and re-establish field markers after the annual flooding of the Nile had swept them away. The A’h-mosè or Rhind mathematical papyrus in the British Museum (dating between 1750 and 1580 bc) is an important source of such information.
Knowledge of cartography in ancient Greece is severely hampered by a complete lack of artefacts. All that can be gleaned is from allusions to the making and use of maps either in contemporary writings or, more usually, in derivative summaries written hundreds of years later. The main sources are the works of Aristotle, Eratosthenes, Strabo, Cleomedes, and Ptolemy.
The prevailing view of the world in archaic Greece and Mesopotamia was of a flat disc surrounded by water, a concept described in Homer’s Iliad and reflected in the Babylonian world map of about 500 bc. Reconstructions of the world map of Anaximander of Miletus or Hecataeus (both in the 6th century bc) usually follow this form. Around 500 bc the concept of a spherical Earth is traditionally associated with the authority of the school of Pythagoras. About this time, there is also some evidence that even the public began to be aware of the idea of a map of the Earth as an instrument for measuring land. Otherwise, it is difficult to explain the passage in The Clouds (423 bc) by Aristophanes that clearly refers to both. Terrestrial and celestial cartography of the Earth used the theories and methods of astronomical cartography and a small industry making celestial maps and globes grew up in the 4th century bc, based on a celestial globe of Eudoxus of Cnidus and an interpretative book, the Phaenomena, known today only through a poetic version by Aratus of Soli. The star positions in this poem were systematically corrected by Hipparchus in the mid-2nd century bc in his Commentary on Aratus. Hipparchus also compiled a star catalogue and is credited with the use of astronomically determined latitudes to determine positions on the terrestrial globe, the division of a circle into 360°, and the conformal stereographic projection in star mapping. Ideas of the division of the Earth into climatic zones, habitable and uninhabitable, can be traced to the works of Aristotle in the mid-4th century bc, particularly On the Heavens and the Meteorology. Aristotle also provided empirical proofs that the Earth is a sphere.
In the Hellenistic Age from the 4th to 1st centuries bc we find references to the mapping of the oikoumene (or known inhabited portion of the ge, or world). This was commonly regarded as being rectangular, twice as long (west to east) as broad (north to south), and divided by two major axes, the diaphragma or Ionian equator running west to east at the latitude of the Pillars of Hercules and Rhodes (about 36° north) and a perpendicular to the diaphragma running north to south through Rhodes, Alexandria, and Syene (Aswan; in fact these cities do not lie along a straight north-south axis). This structure can be traced to Dicaearchus and was built on in about 240 bc by Eratosthenes who, according to the accounts of Strabo in the early 1st century bc and Cleomedes in the 2nd century ad, proposed calculating distances along other key parallels of latitude and between other key meridians of longitude. There is no evidence, however, that Eratosthenes made a map showing these, or whether he even conceived of them as lines. Eratosthenes’s calculations were based on the famous empirical calculation of the circumference of the Earth based on observations of the angle of shadows cast by the Sun on the summer solstice at Syene (where there was no shadow, and which he designated the starting point of his great circle) and Alexandria (where the shadow was about 7°, or 1/50th of a circle away). Knowing the distance between them to be 5,000 stades, Eratosthenes calculated the Earth’s circumference as 250,000 stades (i.e., 50 x 5,000). Owing to uncertainty about the exact length a stade represents (somewhere in the range of 158 to 185 m/519 to 607 ft) this could translate to a distance between 39,500 and 46,250 km (24,545 and 28,740 mi); the Earth’s circumference is usually quoted today at about 40,075 km (24,903 mi).
Much of what we know about Hellenistic Greek mathematical geography was summarized in the 17 books of Strabo’s Geography, but it was two of the treatises of Claudius Ptolemaeus, better known as Ptolemy, that proposed an influential structure for making maps of the inhabited world. The first of these was the Mathematical Syntaxis (often known by its Arabic title as the Almagest), an astronomical compendium in which Ptolemy seeks to improve on Hipparchus’ star catalogue and explain the movement of the stars and planets. It also includes a section on how to make a celestial globe and proposes that Ptolemy’s astronomical scheme of plotting stars can also be applied to mapping the Earth. He explains that he will be writing a work on geography in which the distances of cities east or west of the Alexandrian meridian could be plotted. The Geography was written about 20 years later, where the prime meridian actually proposed went through the Fortunate Isles (the Canary Islands), the westernmost known part of the inhabited world. Ptolemy discusses the difference between making maps of the world (geography) and maps of regions (chorography), stresses the need for astronomical observations of latitude and longitude (a doctrine that he was hardly in a position to follow because of the lack of such observations at the time), and proposes several map projections to improve on the rectangular projection of the Phoenician geographer Marinus of Tyre (which he criticizes as severely distorting the length of parallels in higher latitudes). The work also contained a list of coordinate tables listing the latitude and longitude of cities and other features.