A map is a visual representation of an area—a symbolic depiction highlighting relationships between elements of that space such as objects, regions, and themes.
A celestial map from the 17th century, by the Dutch cartographer Frederik de Wit.
Cartography, or map-making is the study and, often, practice, of crafting representations of the Earth upon a flat surface (see History of cartography), and one who makes maps is called a cartographer.
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 BritishOrdnance Survey (now a civilian government agency internationally renowned for its comprehensively detailed work).
Orientation of maps
The Hereford Mappa Mundi, about 1300, Hereford Cathedral, England. A classic "T-O" map with Jerusalem at centre, east toward the top, Europe the bottom left and Africa on the right.
The term orientation refers to the relationship between directions on a map and compass directions. The word orient is derived from oriens, meaning east. In the Middle Ages many maps, including the T and O maps, were drawn with east at the top. Today the most common, but far from universal, cartographic convention is that North is at the top of a map. Examples of maps not oriented to north are:
Polar maps of the Arctic or Antarctic regions are conventionally centered on the pole, in which case the direction north would be towards or away from the center of the map, respectively.
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.
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 elevation (or depression). These values are often represented, along with other characteristics, and depending on the scale of the map, in the form of Isolines. Isolines on a map or chart indicate a constant value such as temperature, or rainfall. Depending on the type of a map, alternative representations of elevation (or depression) exist as well.
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.
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.
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.
To communicate spatial information effectively, features such as rivers, lakes, cities and so on need to be labeled. Over centuries cartographers perfected the art of placing names on even the densest of maps. Text placement or name placement can get mathematically very complex as the number of labels and map density increases. Therefore, text placement is time-consuming and labor-intensive, which is why automatic label placement makes the life of cartographers and GIS users easier when it comes to labeling maps [1], [2].
Footnotes
^ Imhof, E., “Die Anordnung der Namen in der Karte,” Annuaire International de Cartographie II, Orell-Füssli Verlag, Zürich, 93-129, 1962.
^ Freeman, H.,, Map data processing and the annotation problem, Proc. 3rd Scandinavian Conf. on Image Analysis, Chartwell-Bratt Ltd. Copenhagen, 1983.
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,
Ahn, J. and Freeman, H., “A program for automatic name placement,” Proc. AUTO-CARTO 6, Ottawa, 1983. 444-455.
Freeman, H., “Computer Name Placement,” ch. 29, in Geographical Information Systems, 1, D.J. Maguire, M.F. Goodchild, and D.W. Rhind, John Wiley, New York, 1991, 449-460.
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mappery A diverse collection of real life maps contributed by map lovers worldwide. Includes city tourist maps, college campus maps, park maps, historical maps, and many other types.
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