Portal:Atlas/Selected article

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Portal:Atlas/Selected article/1
A world map by Johannes Kepler

Cartography or mapmaking is the study and practice of making representations of the Earth on a flat surface. The discipline of cartography combines science, aesthetics, and technical ability to create a balanced and readable representation that is capable of communicating information effectively and quickly. Cartographic representation involves the use of symbols and lines to illustrate geographic phenomena. This can aid in visualizing space in an abstract and portable format.

Functioning as tools, maps communicate spatial information by making it visible. Spatial information is acquired from measurement of space and can be stored in a database, from which it can be extracted for a variety of purposes. Current trends in this field are moving away from analog methods of mapmaking and toward the creation of increasingly dynamic, interactive maps that can be manipulated digitally.



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Global view of visible satellite imagery and topography

A geographic information system (GIS) is a system for capturing, storing, analyzing and managing data and associated attributes which are spatially referenced to the earth. In the strictest sense, it is a computer system capable of integrating, storing, editing, analyzing, sharing, and displaying geographically-referenced information. In a more generic sense, GIS is a tool that allows users to create interactive queries, analyze the spatial information, edit data, maps, and present the results of all these operations. Geographic information science is the science underlying the geographic concepts, applications and systems.

Geographic information system technology can be used for scientific investigations, resource management, asset management, Environmental Impact Assessment, Urban planning, cartography, criminology, history, sales, marketing, and logistics.



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Animated Dymaxion projection

A map projection is any method used in cartography to represent the two-dimensional curved surface of the earth or other body on a plane. The term "projection" here refers to any function defined on the earth's surface and with values on the plane, and not necessarily a geometric projection.

Flat maps could not exist without map projections, because a sphere cannot be laid flat over a plane without distortions. One can see this mathematically as a consequence of Gauss's Theorema Egregium. Flat maps can be more useful than globes in many situations: they are more compact and easier to store; they readily accommodate an enormous range of scales; they are viewed easily on computer displays; they can facilitate measuring properties of the terrain being mapped; they can show larger portions of the earth's surface at once; and they are cheaper to produce and transport. These useful traits of flat maps motivate the development of map projections.



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Topographic map of Europe

Topography is the study of Earth's surface features or those of planets, moons, and asteroids. In a broader sense, topography is concerned with local detail in general, including not only relief but also vegetative and human-made features, and even local history and culture. This meaning is less common in America, where topographic maps with elevation contours have made "topography" synonymous with relief. The older sense of Topography as the study of place still has currency in Europe.

For the purposes of this article, topography specifically involves the recording of relief or terrain, the three-dimensional quality of the surface, and the identification of specific landforms. This is also known as geomorphometry. In modern usage, this involves generation of elevation data in electronic form. It is often considered to include the graphic representation of the landform on a map by a variety of techniques, including contour lines, Hypsometric tints, and relief shading.



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Hereford mappa mundi

Mappa mundi is a general term used to describe Medieval European maps of the world. These maps ranged in size and complexity from simple schematic maps an inch or less across, to elaborate wall maps, the largest of which was 11 ft. (3.5 m.) in diameter. The term derives from the Medieval Latin words mappa (cloth or chart) and mundi (of the world). Approximately 1,100 mappae mundi are known to have survived from the Middle Ages. Of these, some 900 are found illustrating manuscripts and the remainder exist as stand-alone documents.

To modern eyes, mappae mundi can look superficially primitive and inaccurate. However, mappae mundi were never meant to be used as navigational charts and they make no pretense of showing land and water proportionately. Rather, mappae mundi were schematic and were meant to illustrate different principles. The simplest mappae mundi were diagrams meant to preserve and illustrate classical learning easily.



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Screenshot of NASA World Wind

A virtual globe is a 3D software model or representation of the Earth or another world. A virtual globe provides the user with the ability to freely move around in the virtual environment by changing the viewing angle and position. Compared to a conventional globe, virtual globes have the additional capability of representing many different views on the surface of the Earth. These views may be of geographical features, man-made features such as roads and buildings or abstract representations of demographic quantities such as population. The first widely publicized virtual globe was Google Earth.

Virtual globes may be used for study or navigation (by connecting to a GPS device) and their design varies considerably according to their purpose. Those wishing to portray a visually accurate representation of the Earth often use satellite image servers and are capable not only of rotation but also zooming and sometimes horizon tilting.



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Ptolemy's world map

The Geographia is Ptolemy's main work besides the Almagest. It is a compilation of what was known about the world's geography in the Roman Empire of the 2nd century. Ptolemy relied mainly on the work of an earlier geographer, Marinos of Tyre, and on gazetteers of the Roman and ancient Persian empire, but most of his sources beyond the perimeter of the Empire were unreliable.

Ptolemy also devised and provided instructions on how to create maps both of the whole inhabited world (oikoumenè) and of the Roman provinces. In the second part of the Geographia he provided the necessary topographic lists, and captions for the maps. His oikoumenè spanned 180 degrees of longitude from the Canary islands in the Atlantic Ocean to China, and about 80 degrees of latitude from the Arctic to the East Indies and deep into Africa; Ptolemy was well aware that he knew about only a quarter of the globe.



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Condensed explanation of Mercator-projection maps

The Mercator projection is a cylindrical map projection presented by the Flemish geographer and cartographer Gerardus Mercator, in 1569. It became the standard map projection for nautical purposes because of its ability to represent lines of constant course, known as rhumb lines or loxodromes, as straight segments. While the linear scale is constant in all directions around any point, thus preserving the angles and the shapes of small objects (which makes the projection conformal), the Mercator projection distorts the size and shape of large objects, as the scale increases from the Equator to the poles, where it becomes infinite. Mercator's 1569 edition was a large planisphere measuring 202 by 124 cm, printed in eighteen separate sheets.

The development of the Mercator projection represented a major breakthrough in the nautical cartography of the 16th century. However, it was much ahead of its time, since the old navigational and surveying techniques were not compatible with its use in navigation. Only in the middle of the 18th century, after the marine chronometer was invented and the spatial distribution of magnetic declination was known, could the Mercator projection be fully adopted by navigators.



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A compass rose

A compass rose is a figure displaying the orientation of the cardinal directions, north, south, east and west on a map or nautical chart. It is also the term for the graduated markings found on the traditional magnetic compass. Today the use and idea of a compass rose is found on or featured in almost all navigation systems, including nautical charts, NDB and VOR systems, some GPS sets and similar.

The "rose" term arises from the fairly ornate figures used with early compasses. A fleur-de-lis figure, evolved from the initial T in the north wind's name Tramontane, is sometimes used to indicate the north direction.

Early roses were depicted with 12 points at 30° each, as was favored by the Romans. In the Middle Ages map makers moved to the 16-point rose complaining that sailors did not have the education to understand the previous design. The earliest 32-point compass rose was developed by Arab navigators during the Middle Ages.



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Digital surface analysis of the United States
Web mapping is the process of designing, implementing, generating and delivering maps on the World Wide Web. The use of the web as a dissemination medium for maps can be regarded as a major advancement in cartography and opens many new opportunities, such as realtime maps, cheaper dissemination, more frequent and cheaper updates of data and software, personalized map content, distributed data sources and sharing of geographic information. It also implicates many challenges due to technical restrictions (low display resolution and limited bandwidth, in particular with mobile computing devices, many of which are physically small, and use slow wireless Internet connections), copyright and security issues, reliability issues and technical complexity. While the first web maps were primarily static, due to technical restrictions, today's web maps can be fully interactive and integrate multiple media. This means that both web mapping and web cartography also have to deal with interactivity, usability and multimedia issues.



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Map of Earth showing lines of latitude (horizontally) and longitude (vertically)

A geographic coordinate system enables every location on the Earth to be specified in three coordinates, using mainly a spherical coordinate system. The Earth is not a sphere, but an irregular shape approximating an ellipsoid; the challenge is to define a coordinate system that can accurately state each topographical feature as an unambiguous set of numbers.

Latitude is the angle from a point on the Earth's surface and the equatorial plane, measured from the centre of the sphere. The north pole is 90° N; the south pole is 90° S. The 0° parallel of latitude is designated the equator. The equator is the fundamental plane of all geographic coordinate systems. The equator divides the globe into Northern and Southern Hemispheres. Longitude is the angle east or west of a reference meridian between the two geographical poles to another meridian that passes through an arbitrary point. All meridians are halves of great circles, and are not parallel. They converge at the north and south poles.



Portal:Atlas/Selected article/12
NOAA continental US weather forecast map
A weather map is used to display an overview of one or more atmospheric variables at a specific time in the free atmosphere. They are used for the analysis and display of observations and computer analyses, including forecast fields derived by computer models. Maps using isotherms show temperature gradients, which can help locate weather fronts. Isotach maps, analyzing lines of equal wind speed, on a constant pressure surface of 300 mb or 250 mb show where the jet stream is located. Two-dimensional streamlines based on wind speeds at various levels show areas of convergence and divergence in the wind field, which are helpful in determining the location of features within the wind pattern. A popular type of surface weather map is the surface weather analysis, which plots isobars to depict areas of high pressure and low pressure. Special weather maps in aviation show areas of icing and turbulence.



Portal:Atlas/Selected article/13
Portion of an electronic chart of the Bering Strait

A nautical chart is a graphic representation of a maritime area and adjacent coastal regions. Depending on the scale of the chart, it may show depths of water and heights of land (topographic map), natural features of the seabed, details of the coastline, navigational hazards, locations of natural and man-made aids to navigation, information on tides and currents, local details of the Earth's magnetic field, and man-made structures such as harbors, buildings and bridges. Nautical charts are essential tools for marine navigation; many countries require vessels, especially commercial ships, to carry them. Nautical charting may take the form of charts printed on paper or computerised electronic navigational charts.

Conventional nautical charts are printed on large sheets of paper at a variety of scales. Electronic navigational charts, which use computer software and electronic databases to provide navigation information, can augment or in some cases replace paper charts, though most mariners carry paper charts as a back up in case the electronic charting system fails.



Portal:Atlas/Selected article/14

Pictorial maps are a category of maps that are also loosely called illustrated maps, panoramic maps, perspective maps, bird’s-eye view maps and Geopictorial maps amongst others.

In contrast to the regular road map, Atlas or topographic cartography, pictorial maps depict a given territory with a more artistic rather than technical style. The cartography can be a sophisticated 3-D perspective landscape or a simple map graphic enlivened with illustrations of buildings, people and animals. They can feature all sorts of varied topics like historical events, legendary figures or local agricultural products and cover anything from an entire continent to a college campus. Drawn by specialized artists and illustrators, pictorial maps are a rich, centuries-old tradition and a diverse art form that ranges from cartoon maps on restaurant placemats to treasured art prints in museums. Pictorial maps usually show an area as if viewed from above at an oblique angle. They are not generally drawn to scale[disambiguation needed] in order to show street patterns, individual buildings, and major landscape features in perspective.



Portal:Atlas/Selected article/15
Topographic map with isohypses of height

A contour line of a function of two variables is a curve along which the function has a constant value. In cartography, a contour line joins points of equal elevation above a given level, such as mean sea level. A contour map is a map illustrated with contour lines, for example a topographic map, which thus shows valleys and hills, and the steepness of slopes. The contour interval of a contour map is the difference in elevation between successive contour lines.

Contour lines are curved or straight lines on a map describing the intersection of a real or hypothetical surface with one or more horizontal planes. The configuration of these contours allows map readers to infer relative gradient of a parameter and estimate that parameter at specific places. Contour lines may be either traced on a visible three-dimensional model of the surface, as when a photogrammetrist viewing a stereo-model plots elevation contours, or interpolated from estimated surface elevations, as when a computer program threads contours through a network of observation points of area centroids. In the latter case, the method of interpolation affects the reliability of individual isolines and their portrayal of slope, pits and peaks.



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A polar grid

In mathematics, the polar coordinate system is a two-dimensional coordinate system in which each point on a plane is determined by an angle and a distance. The polar coordinate system is especially useful in situations where the relationship between two points is most easily expressed in terms of angles and distance; in the more familiar Cartesian or rectangular coordinate system, such a relationship can only be found through trigonometric formulation.

As the coordinate system is two-dimensional, each point is determined by two polar coordinates: the radial coordinate and the angular coordinate. The radial coordinate (usually denoted as r) denotes the point's distance from a central point known as the pole (equivalent to the origin in the Cartesian system). The angular coordinate (also known as the polar angle or the azimuth angle, and usually denoted by θ or t) denotes the positive or anticlockwise (counterclockwise) angle required to reach the point from the 0° ray or polar axis (which is equivalent to the positive x-axis in the Cartesian coordinate plane).



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