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Map
For other uses, see Map (disambiguation).

A map is a simplified depiction of a space, a navigational aid which highlights relations between objects within that space. Most usually a map is a two-dimensional, geometrically accurate representation of a three-dimensional space. The science and art of map-making is cartography.

Introduction

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. [Harvey 2000, p. 142].

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.

Because maps are abstract representations of the world they are not neutral documents and must be carefully interpreted. 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 conceit is elaborated in a one-paragraph story by Jorge Luis Borges and Adolfo Bioy Casares, 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

Conventionally, on most geometrically accurate maps text is upright when the map is oriented with the north up, hence north is identified with the top of a sheet.

Maps that don't put north at the top:

  1. polar maps
  2. Dymaxion maps
  3. Some rectangular maps produced in Australia show the south pole at the top. To someone used to seeing the map the other way around, this map may appear to be "upside down". These are primarily intended as novelty and tourist maps.
  4. 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.
  5. Medieval European T and O maps such as the Hereford Mappa Mundi were centred on Jerusalem, with East at the top.

If a person is located at an identifiable point within the area of such a map, then the map can be oriented in such a way that every point on the map lies in the same direction as the corresponding point in reality. The practice of navigating in this way is orienteering.

For a vertically positioned map representing a horizontal area true orientation is not possible, of course, but it is sometimes approximated by putting the forward direction up.

Occasionally a map is on a ceiling, correctly showing directions; in that case, looking up we have in clockwise direction forward, left, backward, and right. If the map is prepared on a table, to be attached to the ceiling, then on the table it is a mirror image of a normal map.

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 1:25,000, meaning that 1 of any unit of measurement on the map corresponds to 25,000 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 provide a useful tool to 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.


World maps and projections

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.

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). 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 by satellite the position of the user.

From the computer scientist's standpoint, zooming in entails one or a combination of:

  1. replacing the map by a more detailed one
  2. enlarging the same map without enlarging the pixels, hence show more detail
  3. 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 display, 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 that interpolation is performed.

For example:

  • 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).

References

  • 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 0226079872]
  • Miles Harvey, The Island of Lost Maps: A True Story of Cartographic Crime. New York : Random House, 2000. [ISBN 0767908260, cited above; also ISBN 0375501517]
  • Mark Monmorier, How to Lie with Maps, [ISBN 0226534219]
  • O'Connor, J.J. and E.F. Robertson, The History of Cartography (http://www-gap.dcs.st-and.ac.uk/~history/HistTopics/Cartography.html). Scotland : St. Andrews University, 2002. http://www-gap.dcs.st-and.ac.uk/~history/HistTopics/Cartography.html

External links


Note that map services with various zoom levels sometimes show a new map item, such as a new bridge, only on a smaller-scale map and not on an available larger scale map, because the latter is not as often updated, see e.g. the Tuas Second Link on [7] (http://www.multimap.com/p/browse.cgi?scale=100000&lon=103.85&lat=1.3&scale=2000000), and larger scales which do not show it.
See also:
| George Bradshaw | Atlas (cartography) | Geologic map | Topographic map | World map | Plat | Juan de la Cosa |
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