Map

   

For alternative meanings see Map (disambiguation)

A map is a two-dimensional representation of a three-dimensional space. The science of making maps is called cartography.

Introduction

Mapmaking dates back at least to the Stone Age and appears to predate written language by several millennia. On 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].

Early maps were vague and there was often controversy as to where to centre the map - one world map, for instance, has Jerusalem at the centre. The purpose of such maps seem to not be intended as geographic, but rather to show a history with regards to that geography. The early ship navigation charts were quite similar to modern maps in accuracy with the exception of unknown areas.

Many maps have a scale, determining how large objects on the map are in relation to their actual size. A larger scale shows more detail, thus requiring a larger map to show the same area. Some, though, are not drawn to scale - a famous example being the London Underground map.

If the map covers a large area of the surface of a globe, such as the Earth, it also has a projection, a way of translating the three-dimensional real surface of the geoid to a two-dimensional picture. One commonly used for navigation is the Mercator Projection; other popular projections are polar and a variety of equal-area projections.

The features shown on a map vary according to its purpose. For example, a road map may or may not show railroads, and if it does, it may show them less clearly than highways.

Maps can be political or geographical. The most important purpose of the political map is to show territorial borders; the purpose of the geographical 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.

Many surveying projects have been carried out by the military. An example of this the British Ordnance Survey (which now is a civilian government agency).

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".

Electronic maps

For maps on a computer display, e.g. from the web or locally stored on CD-ROM or harddisk, zooming in means enlarging the scale, either by showing a smaller area in the same viewing window or by showing the same area in a larger viewing window, and one of the following:

  • replace the map by a more detailed one
  • enlarge the same map without enlarging the pixels, hence show more detail
  • enlarge 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 CRT), then replacing a pixel by a rectangle of pixels does show more detail.

Combinations are possible, e.g. the second applying for text and the third for the outline of a map feature such as a forest, a building etc. Also the map may have layers which are partly raster graphics and partly vector graphics.

For a single raster graphics image the second applies until the pixels in the image file correspond to the pixels of the display; on further zooming in, the third applies.

For a PDF-file typically the second applies. The increase in detail is, of course, limited to the information contained in the file: enlarging a curve it may eventually become a series of straight line segments, or other standard geometric figures such as arcs of circles.

A variation of the third possibility is that interpolation is performed.

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. A variation of the first possibility above is that more text is displayed (such as more town names), but that for the rest of the image the second applies.

See also Webpage#Graphics, Portable Document Format#Layers.

Web maps are typically handled by a Geographic information system which does the spatial data processing necessary to handle different coordinate system and spatial relations between different kinds of data. GIS does a lot more than make maps, though.

Links and references

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]

See also

External links



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