A map is a simplified depiction of a space which highlights relations between components (objects, regions) of that space. Most usually a map is a two-dimensional, geometrically accurate representation of a three-dimensional space; e.g., a geographical map. More generally, maps can be devised to represent any local property of the world or part of it, or any other space, such as the brain (see Brain mapping).
 Geographical maps
A celestial map from the 17th century, by the Dutch cartographer Frederik de Wit.
The science and art of map-making is cartography; see that page for further discussion of the history of maps and map-making.
Map-making dates back to the Stone Age and appears to predate written language by several millennia. One of the oldest surviving maps is painted on a wall of the Catal Huyuk settlement in south-central Anatolia (now Turkey); it dates from about 6200 BC.  One who makes maps professionally or privately is called a cartographer.
While we tend to think of maps today as products of a rationalistic, scientific world-view, maps also have a mythic quality. Pre-modern maps, and mapping traditions outside the Western tradition, often merge geography with non-scientific cosmography, showing the relationship of the viewer to the universe. Medieval "T-O" maps, for example, show Jerusalem at the centre of the world, and in some cases related the "body" of the Earth to the body of Christ. By contrast, navigational (or "Portolan") charts of the Mediterranean from the same period are remarkably accurate. Even today, maps can be powerful rhetorical tools beyond their purely practical value, and this has been the source of much fruitful map criticism over the last twenty years, notably in the works of J.B. Harley, Mark Monmonier, and Denis Wood.
Physical map of the Earth
Geographic maps are abstract representations of the world. It is, of course, this abstraction that makes them useful. Lewis Carroll made this point humorously in Sylvie and Bruno with his mention of a fictional map that had "the scale of a mile to the mile". A character notes some practical difficulties with this map and states that "we now use the country itself, as its own map, and I assure you it does nearly as well". This concept is elaborated in a one-paragraph story by Jorge Luis Borges, generally known in English as "On Exactitude in Science".
Road maps are perhaps the most widely used maps today, and form a subset of navigational maps, which also include aeronautical and nautical charts, railroad network maps, and hiking and bicycling maps. In terms of quantity, the largest number of drawn map sheets is probably made up by local surveys, carried out by municipalities, utilities, tax assessors, emergency services providers, and other local agencies. Many national surveying projects have been carried out by the military, such as the British Ordnance Survey (now a civilian government agency internationally renowned for its comprehensively detailed work).
 Orientation of maps
The most common cartographic convention is that North is at the top of a map. This is far from universal, however:
- Polar maps of the Arctic or Antarctic regions are conventionally centered on the pole, making "north is up" meaningless.
- Azimuthal or Gnomonic projections are often used in planning air routes, centered on specific origin points.
- Richard Edes Harrison produced a striking series of maps during and after World War II for Fortune magazine. These used "bird's eye" projections to emphasize globally strategic "fronts" in the air age, pointing out proximities and barriers not as apparent on a conventional rectangular projection of the world.
- Buckminster Fuller's Dymaxion maps are based on a projection of the Earth's sphere onto an icosahedron. The resulting triangular pieces may be arranged in any order or orientation.
- Maps from non-Western traditions are oriented a variety of ways. Old maps of Edo show the Japanese imperial palace as the "top," but also at the centre, of the map. Labels on the map are oriented in such a way that you cannot read them properly unless you put the imperial palace above your head.
- Medieval European T and O maps such as the Hereford Mappa Mundi were centred on Jerusalem with east at the top. Indeed, prior to the reintroduction of Ptolemy's Geography to Europe around 1400, there was no single convention in the West. Portolan charts, for example, are oriented to the shores they describe.
- Route and channel maps have traditionally been oriented to the road or waterway they describe.
 Scale and accuracy
Many but not all maps are drawn to a scale, allowing the reader to infer the actual sizes of, and distances between, depicted objects. A larger scale shows more detail, thus requiring a larger map to show the same area. For example, maps designed for the hiker are often scaled at the ratio 1:24,000, meaning that 1 of any unit of measurement on the map corresponds to 24,000 of that same unit in reality; while maps designed for the motorist are often scaled at 1:250,000. Maps which use some quality other than physical area to determine relative size are called cartograms.
A famous example of a map without scale is the London Underground map, which best fulfils its purpose by being less physically accurate and more visually communicative to the hurried glance of the commuter. This is not a cartogram (since there is no consistent measure of distance) but a topological map that also depicts approximate bearings. The simple maps shown on some directional road signs are further examples of this kind.
In fact, most commercial navigational maps, such as road maps and town plans, sacrifice an amount of accuracy in scale to deliver a greater visual usefulness to its user, for example by exaggerating the width of roads. With the end-user similarly in mind, cartographers will censor the content of the space depicted by a map in order to provide a useful tool for that user. For example, a road map may or may not show railroads, and if it does, it may show them less clearly than highways.
Some maps such as topographical maps show constant values such as average temperature, these are often represented, along with other characteristics, depending on the scale of the map, in the form of Isolines. Isolines are often on a map or chart along which there is constant value (temperature, pressure, or rainfall).
 World maps and projections
Map of large underwater features. (1995, NOAA
Maps of the world or large areas are often either 'political' or 'physical'. The most important purpose of the political map is to show territorial borders; the purpose of the physical is to show features of geography such as mountains, soil type or land use. Geological maps show not only the physical surface, but characteristics of the underlying rock, fault lines, and subsurface structures.
Maps that depict the surface of the Earth also use a projection, a way of translating the three-dimensional real surface of the geoid to a two-dimensional picture. Perhaps the best-known world-map projection is the Mercator Projection, originally designed as a form of nautical chart.
Airplane pilots use aeronautical charts based on a Lambert conformal conic projection, in which a cone is laid over the section of the earth to be mapped. The cone intersects the sphere (the earth) at one or two parallels which are chosen as standard lines. This allows the pilots to plot a great-circle route approximation on a flat, two-dimensional chart.
 Electronic maps
From the last quarter of the 20th century, the indispensable tool of the cartographer has been the computer. Much of cartography, especially at the data-gathering survey level, has been subsumed by Geographic Information Systems (GIS). The functionality of maps has been greatly advanced by technology allowing, for example, the superimposition of spatially located variables onto existing geographical maps. Having local information such as rainfall level, distribution of wildlife, or demographic data integrated within the map makes for more efficient analysis and better decision making. In the pre-electronic age such superimposition of data led to Dr. John Snow discovering the cause of cholera. Today, it is used by agencies as diverse as wildlife conservationists and militaries around the world.
Even when GIS is not involved, most cartographers now use a variety of computer graphics programs to generate new maps.
Interactive, computerised maps are commercially available, allowing users to zoom in or zoom out (respectively meaning to increase or decrease the scale), sometimes by replacing one map with another of different scale, centred where possible on the same point. In-car satellite navigation systems are computerised maps with route-planning and advice facilities which monitor the user's position with the help of satellites.
From the computer scientist's point of view, zooming in entails one or a combination of:
- replacing the map by a more detailed one
- enlarging the same map without enlarging the pixels, hence showing more detail by removing less information compared to the less detailed version
- enlarging the same map with the pixels enlarged (replaced by rectangles of pixels); no additional detail is shown, but, depending on the quality of one's vision, possibly more detail can be seen; if a computer display does not show adjacent pixels really separate, but overlapping instead (this does not apply for an LCD, but may apply for a cathode ray tube), then replacing a pixel by a rectangle of pixels does show more detail. A variation of this method is interpolation.
- Typically (2) applies to a Portable Document Format (PDF) file. The increase in detail is, of course, limited to the information contained in the file: enlargement of a curve may eventually result in a series of standard geometric figures such as straight lines or arcs of circles.
- (2) may apply to text and (3) to the outline of a map feature such as a forest or building.
- (1) may apply to the text (displaying labels for more features), while (2) applies to the rest of the image. Text is not necessarily enlarged when zooming in. Similarly, a road represented by a double line may or may not become wider when one zooms in.
- The map may also have layers which are partly raster graphics and partly vector graphics. For a single raster graphics image (2) applies until the pixels in the image file correspond to the pixels of the display, thereafter (3) applies.
See also Webpage (Graphics), PDF (Layers), Mapquest, Google Maps, Google Earth or Yahoo! Maps.
- ^ *Miles Harvey, The Island of Lost Maps: A True Story of Cartographic Crime. New York : Random House, 2000 ISBN 0-7679-0826-0, cited above; also ISBN 0-375-50151-7
- David Buisseret, ed., Monarchs, Ministers and Maps: The Emergence of Cartography as a Tool of Government in Early Modern Europe. Chicago: University of Chicago Press, 1992, ISBN 0-226-07987-2
- Mark Monmonier, How to Lie with Maps, ISBN 0-226-53421-9
- O'Connor, J.J. and E.F. Robertson, The History of Cartography. Scotland : St. Andrews University, 2002.
- Denis E. Cosgrove (ed.) Mappings. Reaktion Books, 1999 ISBN 1-86189-021-4
 See also
- Map design and types
- Modern maps
- Map history
- Related Topics
 External links
 Map discussion and history
 Map link sites
 Modern maps and atlases online
World Maps and Atlases:
 Antique and historical maps online
 Online map creation tools