A map is a symbolic depiction emphasizing relationships between elements of some space, such as objects, regions, or themes.

Many maps are static, fixed to paper or some other durable medium, while others are dynamic or interactive. Although most commonly used to depict geography, maps may represent any space, real or fictional, without regard to context or scale, such as in brain mapping, DNA mapping, or computer network topology mapping. The space being mapped may be two dimensional, such as the surface of the earth, three dimensional, such as the interior of the earth, or even more abstract spaces of any dimension, such as arise in modeling phenomena having many independent variables.

Although the earliest maps known are of the heavens, geographic maps of territory have a very long tradition and exist from ancient times. The word "map" comes from the medieval Latin Mappa mundi, wherein mappa meant napkin or cloth and mundi the world. Thus, "map" became the shortened term referring to a two-dimensional representation of the surface of the world.

World Map 1689
World map by Gerard van Shagen, Amsterdam, 1689
Map of the world by the US Gov as of 2016
World map from 2016 CIA World Factbook

Geographic maps

Planisphæri cœleste
A celestial map from the 17th century, by the cartographer Frederik de Wit

Cartography or map-making is the study and 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 British Ordnance Survey: a civilian government agency, internationally renowned for its comprehensively detailed work.

In addition to location information, maps may also be used to portray contour lines indicating constant values of elevation, temperature, rainfall, etc.

Orientation of maps

Hereford Mappa Mundi 1300
The Hereford Mappa Mundi from about 1300, Hereford Cathedral, England, is a classic "T-O" map with Jerusalem at centre, east toward the top, Europe the bottom left and Africa on the right.

The orientation of a map is the relationship between the directions on the map and the corresponding compass directions in reality. The word "orient" is derived from Latin oriens, meaning east. In the Middle Ages many maps, including the T and O maps, were drawn with east at the top (meaning that the direction "up" on the map corresponds to East on the compass). The most common cartographic convention is that north is at the top of a map.

Maps not oriented with north at the top:

  • 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.
  • Maps of cities bordering a sea are often conventionally oriented with the sea at the top.
  • Route and channel maps have traditionally been oriented to the road or waterway they describe.
  • Polar maps of the Arctic or Antarctic regions are conventionally centred on the pole; the direction North would be towards or away from the centre of the map, respectively. Typical maps of the Arctic have 0° meridian towards the bottom of the page; maps of the Antarctic have the 0° meridian towards the top of the page.
  • Reversed maps, also known as Upside-Down maps or South-Up maps, reverse the North is up convention and have south at the top. Ancient Africans including in Ancient Egypt utilised this orientation, as some maps in Brazil do today.[1]
  • 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.

Scale and accuracy

Many maps are drawn to a scale expressed as a ratio, such as 1:10,000, which means that 1 unit of measurement on the map corresponds to 10,000 of that same unit on the ground. The scale statement can be accurate when the region mapped is small enough for the curvature of the Earth to be neglected, such as a city map. Mapping larger regions, where curvature cannot be ignored, requires projections to map from the curved surface of the Earth to the plane. The impossibility of flattening the sphere to the plane without distortion means that the map cannot have constant scale. Rather, on most projections the best that can be attained is accurate scale along one or two paths on the projection. Because scale differs everywhere, it can only be measured meaningfully as point scale per location. Most maps strive to keep point scale variation within narrow bounds. Although the scale statement is nominal it is usually accurate enough for most purposes unless the map covers a large fraction of the earth. At the scope of a world map, scale as a single number is practically meaningless throughout most of the map. Instead, it usually refers to the scale along the equator.

EU Pop2008 1024
Cartogram: The EU distorted to show population distributions as of 2008.

Some maps, called cartograms, have the scale deliberately distorted to reflect information other than land area or distance. For example, this map (at the right) of Europe has been distorted to show population distribution, while the rough shape of the continent is still discernible.

Another example of distorted scale is the famous London Underground map. The basic geographical structure is respected but the tube lines (and the River Thames) are smoothed to clarify the relationships between stations. Near the center of the map stations are spaced out more than near the edges of map.

Further inaccuracies may be deliberate. For example, cartographers may simply omit military installations or remove features solely in order to enhance the clarity of the map. For example, a road map may not show railroads, smaller waterways or other prominent non-road objects, and even if it does, it may show them less clearly (e.g. dashed or dotted lines/outlines) than the main roads. Known as decluttering, the practice makes the subject matter that the user is interested in easier to read, usually without sacrificing overall accuracy. Software-based maps often allow the user to toggle decluttering between ON, OFF and AUTO as needed. In AUTO the degree of decluttering is adjusted as the user changes the scale being displayed.

Map projection

Geographic maps use a projection to translating the three-dimensional real surface of the geoid to a two-dimensional picture. Projection always distorts the surface. There are many ways to apportion the distortion, and so there are many map projections. Which projection to use depends on the purpose of the map.


The various features shown on a map are represented by conventional signs or symbols. For example, colors can be used to indicate a classification of roads. Those signs are usually explained in the margin of the map, or on a separately published characteristic sheet.[2]

Some cartographers prefer to make the map cover practically the entire screen or sheet of paper, leaving no room "outside" the map for information about the map as a whole. These cartographers typically place such information in an otherwise "blank" region "inside" the map—cartouche, map legend, title, compass rose, bar scale, etc. In particular, some maps contain smaller "sub-maps" in otherwise blank regions—often one at a much smaller scale showing the whole globe and where the whole map fits on that globe, and a few showing "regions of interest" at a larger scale in order to show details that wouldn't otherwise fit. Occasionally sub-maps use the same scale as the large map—a few maps of the contiguous United States include a sub-map to the same scale for each of the two non-contiguous states.


To communicate spatial information effectively, features such as rivers, lakes, and cities need to be labeled. Over centuries cartographers have developed 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, so cartographers and GIS users have developed automatic label placement to ease this process.[3][4]

Map types

Ocean gravity map
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 including infrastructure such as roads, railroads and buildings. Topographic maps show elevations and relief with contour lines or shading. Geological maps show not only the physical surface, but characteristics of the underlying rock, fault lines, and subsurface structures.

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 simplifying 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 allows more efficient analysis and better decision making. In the pre-electronic age such superimposition of data led Dr. John Snow to identify the location of an outbreak of cholera. Today, it is used by agencies of the human kind, as diverse as wildlife conservationists and militaries around the world.

Maps-for-free Sierra Nevada
Relief map Sierra Nevada

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, centered where possible on the same point. In-car global navigation satellite 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:

  1. replacing the map by a more detailed one
  2. enlarging the same map without enlarging the pixels, hence showing more detail by removing less information compared to the less detailed version
  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, 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.
A world map in PDF format.

For example:

  • Typically (2) applies to a Portable Document Format (PDF) file or other format based on vector graphics. The increase in detail is 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, arcs of circles or splines.
  • (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 as needed (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, OpenStreetMap or Yahoo! Maps.

Climatic maps

The maps that reflect the territorial distribution of climatic conditions based on the results of long-term observations are called climatic maps. These maps can be compiled both for individual climatic features (temperature, precipitation, humidity) and for combinations of them at the earth's surface and in the upper layers of the atmosphere. Climatic maps afford a very convenient overview of the climatic features in a large region and permit values of climatic features to be compared in different parts of the region. Through interpolation the maps can be used to determine the values of climatic features in any particular spot.

Climatic maps generally apply to individual months and to the year as a whole, sometimes to the four seasons, to the growing period, and so forth. On maps compiled from the observations of ground meteorological stations, atmospheric pressure is converted to sea level. Air temperature maps are compiled both from the actual values observed on the surface of the earth and from values converted to sea level. The pressure field in free atmosphere is represented either by maps of the distribution of pressure at different standard altitudes—for example, at every kilometer above sea level—or by maps of baric topography on which altitudes (more precisely geopotentials) of the main isobaric surfaces (for example, 900, 800, and 700 millibars) counted off from sea level are plotted. The temperature, humidity, and wind on aeroclimatic maps may apply either to standard altitudes or to the main isobaric surfaces.

Isolines are drawn on maps of such climatic features as the long-term mean values (of atmospheric pressure, temperature, humidity, total precipitation, and so forth) to connect points with equal values of the feature in question—for example, isobars for pressure, isotherms for temperature, and isohyets for precipitation. Isoamplitudes are drawn on maps of amplitudes (for example, annual amplitudes of air temperature—that is, the differences between the mean temperatures of the warmest and coldest month). Isanomals are drawn on maps of anomalies (for example, deviations of the mean temperature of each place from the mean temperature of the entire latitudinal zone). Isolines of frequency are drawn on maps showing the frequency of a particular phenomenon (for example, annual number of days with a thunderstorm or snow cover). Isochrones are drawn on maps showing the dates of onset of a given phenomenon (for example, the first frost and appearance or disappearance of the snow cover) or the date of a particular value of a meteorological element in the course of a year (for example, passing of the mean daily air temperature through zero). Isolines of the mean numerical value of wind velocity or isotachs are drawn on wind maps (charts); the wind resultants and directions of prevailing winds are indicated by arrows of different length or arrows with different plumes; lines of flow are often drawn. Maps of the zonal and meridional components of wind are frequently compiled for the free atmosphere. Atmospheric pressure and wind are usually combined on climatic maps. Wind roses, curves showing the distribution of other meteorological elements, diagrams of the annual course of elements at individual stations, and the like are also plotted on climatic maps.

Maps of climatic regionalization, that is, division of the earth's surface into climatic zones and regions according to some classification of climates, are a special kind of climatic map.

Climatic maps are often incorporated into climatic atlases of varying geographic range (globe, hemispheres, continents, countries, oceans) or included in comprehensive atlases. Besides general climatic maps, applied climatic maps and atlases have great practical value. Aeroclimatic maps, aeroclimatic atlases, and agroclimatic maps are the most numerous.

Non-geographical spatial maps

Maps exist of the Solar System, and other cosmological features such as star maps. In addition maps of other bodies such as the Moon and other planets are technically not geographical maps.

Topological maps

Inventory Locations Represented as a Map
In a topological map, like this one showing inventory locations, the distances between locations is not important. Only the layout and connectivity between them matters.

Diagrams such as schematic diagrams and Gantt charts and treemaps display logical relationships between items, rather than geographical relationships. Topological in nature, only the connectivity is significant. The London Underground map and similar subway maps around the world are a common example of these maps.

General-purpose maps

General-purpose maps provide many types of information on one map. Most atlas maps, wall maps, and road maps fall into this category. The following are some features that might be shown on general-purpose maps: bodies of water, roads, railway lines, parks, elevations, towns and cities, political boundaries, latitude and longitude, national and provincial parks. These maps give a broad understanding of location and features of an area. The reader may gain an understanding of the type of landscape, the location of urban places, and the location of major transportation routes all at once.

List of map types

Legal regulation

Some countries required that all published maps represent their national claims regarding border disputes. For example:

  • Within Russia, Google Maps shows Crimea as part of Russia.[5]
  • Both the Republic of India and the People's Republic of China require that all maps show areas subject to the Sino-Indian border dispute in their own favor.[6]

In 2010, the People's Republic of China began requiring that all online maps served from within China be hosted there, making them subject to Chinese laws.[7]

See also

Map designing and types
Map history
Related topics


  1. ^ The orientation of the world in the African thought
  2. ^ Ordnance Survey, Explorer Map Symbols Archived 3 April 2016 at the Wayback Machine; Swisstopo, Conventional Signs Archived 28 May 2008 at the Wayback Machine; United States Geological Survey, Topographic Map Symbols Archived 1 June 2008 at the Wayback Machine.
  3. ^ Imhof, E., “Die Anordnung der Namen in der Karte,” Annuaire International de Cartographie II, Orell-Füssli Verlag, Zürich, 93–129, 1962.
  4. ^ Freeman, H., Map data processing and the annotation problem, Proc. 3rd Scandinavian Conf. on Image Analysis, Chartwell-Bratt Ltd. Copenhagen, 1983.
  5. ^ Chappell, Bill (12 April 2014). "Google Maps Displays Crimean Border Differently In Russia, U.S." Retrieved 6 September 2018.
  6. ^ Wagstaff, Jeremy (23 March 2012). "Google charts a careful course through Asia's maps". Reuters. Retrieved 6 September 2018.
  7. ^ Guanqun, Wang (19 May 2010). "China issues new rules on Internet map publishing". Xinhua News Agency. Archived from the original on 27 May 2016. Retrieved 27 July 2016.
  • 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
  • Denis E. Cosgrove (ed.) Mappings. Reaktion Books, 1999 ISBN 1-86189-021-4
  • Freeman, Herbert, Automated Cartographic Text Placement. White paper.
  • 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.
  • 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.

External links


Cartography (; from Greek χάρτης chartēs, "papyrus, sheet of paper, map"; and γράφειν graphein, "write") is the study and practice of making maps. Combining science, aesthetics, and technique, cartography builds on the premise that reality can be modeled in ways that communicate spatial information effectively.

The fundamental problems of traditional cartography are to:

Set the map's agenda and select traits of the object to be mapped. This is the concern of map editing. Traits may be physical, such as roads or land masses, or may be abstract, such as toponyms or political boundaries.

Represent the terrain of the mapped object on flat media. This is the concern of map projections.

Eliminate characteristics of the mapped object that are not relevant to the map's purpose. This is the concern of generalization.

Reduce the complexity of the characteristics that will be mapped. This is also the concern of generalization.

Orchestrate the elements of the map to best convey its message to its audience. This is the concern of map design.Modern cartography constitutes many theoretical and practical foundations of geographic information systems.


An essay is, generally, a piece of writing that gives the author's own argument — but the definition is vague, overlapping with those of a paper, an article, a pamphlet, and a short story. Essays have traditionally been sub-classified as formal and informal. Formal essays are characterized by "serious purpose, dignity, logical organization, length," whereas the informal essay is characterized by "the personal element (self-revelation, individual tastes and experiences, confidential manner), humor, graceful style, rambling structure, unconventionality or novelty of theme," etc.Essays are commonly used as literary criticism, political manifestos, learned arguments, observations of daily life, recollections, and reflections of the author. Almost all modern essays are written in prose, but works in verse have been dubbed essays (e.g., Alexander Pope's An Essay on Criticism and An Essay on Man). While brevity usually defines an essay, voluminous works like John Locke's An Essay Concerning Human Understanding and Thomas Malthus's An Essay on the Principle of Population are counterexamples.

In some countries (e.g., the United States and Canada), essays have become a major part of formal education. Secondary students are taught structured essay formats to improve their writing skills; admission essays are often used by universities in selecting applicants, and in the humanities and social sciences essays are often used as a way of assessing the performance of students during final exams.

The concept of an "essay" has been extended to other media beyond writing. A film essay is a movie that often incorporates documentary filmmaking styles and focuses more on the evolution of a theme or idea. A photographic essay covers a topic with a linked series of photographs that may have accompanying text or captions.

Fortune 500

The Fortune 500 is an annual list compiled and published by Fortune magazine that ranks 500 of the largest United States corporations by total revenue for their respective fiscal years. The list includes publicly held companies, along with privately held companies for which revenues are publicly available. The concept of the Fortune 500 was created by Edgar P. Smith, a Fortune editor, and the first list was published in 1955. The Fortune 500 is more commonly used than its subset Fortune 100 or superset Fortune 1000.

Geographic coordinate system

A geographic coordinate system is a coordinate system that enables every location on Earth to be specified by a set of numbers, letters or symbols. The coordinates are often chosen such that one of the numbers represents a vertical position and two or three of the numbers represent a horizontal position; alternatively, a geographic position may be expressed in a combined three-dimensional Cartesian vector.

A common choice of coordinates is latitude, longitude and elevation.

To specify a location on a plane requires a map projection.

Geographic information system

A geographic information system (GIS) is a system designed to capture, store, manipulate, analyze, manage, and present spatial or geographic data. GIS applications are tools that allow users to create interactive queries (user-created searches), analyze spatial information, edit data in maps, and present the results of all these operations. GIS (more commonly GIScience) sometimes refers to geographic information science (GIScience), the science underlying geographic concepts, applications, and systems.GIS can refer to a number of different technologies, processes, techniques and methods. It is attached to many operations and has many applications related to engineering, planning, management, transport/logistics, insurance, telecommunications, and business. For that reason, GIS and location intelligence applications can be the foundation for many location-enabled services that rely on analysis and visualization.

GIS can relate unrelated information by using location as the key index variable. Locations or extents in the Earth space–time may be recorded as dates/times of occurrence, and x, y, and z coordinates representing, longitude, latitude, and elevation, respectively. All Earth-based spatial–temporal location and extent references should be relatable to one another and ultimately to a "real" physical location or extent. This key characteristic of GIS has begun to open new avenues of scientific inquiry.

Google Maps

Google Maps is a web mapping service developed by Google. It offers satellite imagery, aerial photography, street maps, 360° panoramic views of streets (Street View), real-time traffic conditions (Google Traffic), and route planning for traveling by foot, car, bicycle and air (in beta), or public transportation.

Google Maps began as a C++ desktop program at Where 2 Technologies. In October 2004, the company was acquired by Google, which converted it into a web application. After additional acquisitions of a geospatial data visualization company and a realtime traffic analyzer, Google Maps was launched in February 2005. The service's front end utilizes JavaScript, XML, and Ajax. Google Maps offers an API that allows maps to be embedded on third-party websites, and offers a locator for urban businesses and other organizations in numerous countries around the world. Google Map Maker allowed users to collaboratively expand and update the service's mapping worldwide but was discontinued from March 2017. However, crowdsourced contributions to Google Maps were not discontinued as the company announced those features will be transferred to the Google Local Guides program.Google Maps' satellite view is a "top-down" or "birds eye" view; most of the high-resolution imagery of cities is aerial photography taken from aircraft flying at 800 to 1,500 feet (240 to 460 m), while most other imagery is from satellites. Much of the available satellite imagery is no more than three years old and is updated on a regular basis. Google Maps used a variant of the Mercator projection, and therefore cannot accurately show areas around the poles. However, in August 2018, the desktop version of Google Maps was updated to show a 3D globe.

The current redesigned version of the desktop application was made available in 2013, alongside the "classic" (pre-2013) version. Google Maps for Android and iOS devices was released in September 2008 and features GPS turn-by-turn navigation along with dedicated parking assistance features. In August 2013, it was determined to be the world's most popular app for smartphones, with over 54% of global smartphone owners using it at least once.In 2012, Google reported having over 7,100 employees and contractors directly working in mapping.

Halo 2

Halo 2 is a 2004 first-person shooter video game developed by Bungie. Released for the Xbox video game console on November 9, 2004, the game is the second installment in the Halo franchise and the sequel to 2001's critically acclaimed Halo: Combat Evolved. A Microsoft Windows version of the game was released on May 31, 2007, developed by an internal team at Microsoft Game Studios known as Hired Gun. The game features a new game engine, as well as using the Havok physics engine; added weapons and vehicles, and new multiplayer maps. The player alternately assumes the roles of the human Master Chief and the alien Arbiter in a 26th-century conflict between the human United Nations Space Command, the genocidal Covenant, and the parasitic Flood.

After the success of Combat Evolved, a sequel was expected and highly anticipated. Bungie found inspiration in plot points and gameplay elements that had been left out of their first game, including multiplayer over the Internet through Xbox Live. Time constraints forced a series of cutbacks in the size and scope of the game, including a cliffhanger ending to the game's campaign mode that left many in the studio dissatisfied. Among Halo 2's marketing efforts was an alternate reality game called "I Love Bees" that involved players solving real-world puzzles.

On release, Halo 2 was the most popular video game on Xbox Live, holding that rank until the release of Gears of War for the Xbox 360 nearly two years later. By June 20, 2006, more than 500 million games of Halo 2 had been played and more than 710 million hours have been spent playing it on Xbox Live; by May 9, 2007, the number of unique players had risen to over five million. Halo 2 is the best-selling first-generation Xbox game with at least 6.3 million copies sold in the United States alone. The game received critical acclaim, with most publications lauding the strong multiplayer component. The campaign however, was the focus of criticism for its cliffhanger ending.

A high-definition remastered version of Halo 2 was released as part of Halo: The Master Chief Collection on November 11, 2014, for the Xbox One titled Halo 2 Anniversary. The collection itself will be released for the Windows in 2019.

Linear map

In mathematics, a linear map (also called a linear mapping, linear transformation or, in some contexts, linear function) is a mapping V → W between two modules (including vector spaces) that preserves (in the sense defined below) the operations of addition and scalar multiplication.

An important special case is when V = W, in which case the map is called a linear operator, or an endomorphism of V. Sometimes the term linear function has the same meaning as linear map, while in analytic geometry it does not.

A linear map always maps linear subspaces onto linear subspaces (possibly of a lower dimension); for instance it maps a plane through the origin to a plane, straight line or point. Linear maps can often be represented as matrices, and simple examples include rotation and reflection linear transformations.

In the language of abstract algebra, a linear map is a module homomorphism. In the language of category theory it is a morphism in the category of modules over a given ring.

List of cities and towns in Colorado

Colorado is a state located in the Western United States. Colorado currently has 271 incorporated municipalities, comprising 196 towns, 73 cities, and two consolidated city and county governments.

List of districts in India

A district (zilā) is an administrative division of an Indian state or territory. In some cases districts are further subdivided into sub-divisions, and in others directly into tehsils or talukas. As of 2019 there are a total of 725 districts, up from the 640 in the 2011 Census of India and the 593 recorded in the 2001 Census of India.District officials include:

District Magistrate or Deputy Commissioner or District Collector, an officer of the Indian Administrative Service, in charge of administration and revenue collection

Superintendent of Police or Senior Superintendent of Police or Deputy Commissioner of Police, an officer belonging to the Indian Police Service, responsible for maintaining law and order

Deputy Conservator of Forests, an officer belonging to the Indian Forest Service, entrusted with the management of the forests, environment and wildlife of the districtEach of these officials is aided by officers from the appropriate branch of the state government.

Most districts have a distinct headquarters; but the districts of Mumbai City, in Maharashtra, and Chennai, in Tamil Nadu, are examples where there is no distinct district headquarters, although there are district collectors.

Mahe of Puducherry is the smallest (9 km2) district of India by area while Kutch of Gujarat is the largest (45,652 km2) district of India by area.


MapReduce is a programming model and an associated implementation for processing and generating big data sets with a parallel, distributed algorithm on a cluster.A MapReduce program is composed of a map procedure (or method), which performs filtering and sorting (such as sorting students by first name into queues, one queue for each name), and a reduce method, which performs a summary operation (such as counting the number of students in each queue, yielding name frequencies). The "MapReduce System" (also called "infrastructure" or "framework") orchestrates the processing by marshalling the distributed servers, running the various tasks in parallel, managing all communications and data transfers between the various parts of the system, and providing for redundancy and fault tolerance.

The model is a specialization of the split-apply-combine strategy for data analysis.

It is inspired by the map and reduce functions commonly used in functional programming, although their purpose in the MapReduce framework is not the same as in their original forms. The key contributions of the MapReduce framework are not the actual map and reduce functions (which, for example, resemble the 1995 Message Passing Interface standard's reduce and scatter operations), but the scalability and fault-tolerance achieved for a variety of applications by optimizing the execution engine. As such, a single-threaded implementation of MapReduce will usually not be faster than a traditional (non-MapReduce) implementation; any gains are usually only seen with multi-threaded implementations on multi-processor hardware. The use of this model is beneficial only when the optimized distributed shuffle operation (which reduces network communication cost) and fault tolerance features of the MapReduce framework come into play. Optimizing the communication cost is essential to a good MapReduce algorithm.MapReduce libraries have been written in many programming languages, with different levels of optimization. A popular open-source implementation that has support for distributed shuffles is part of Apache Hadoop. The name MapReduce originally referred to the proprietary Google technology, but has since been genericized. By 2014, Google was no longer using MapReduce as their primary big data processing model, and development on Apache Mahout had moved on to more capable and less disk-oriented mechanisms that incorporated full map and reduce capabilities.

Mind map

A mind map is a diagram used to visually organize information. A mind map is hierarchical and shows relationships among pieces of the whole. It is often created around a single concept, drawn as an image in the center of a blank page, to which associated representations of ideas such as images, words and parts of words are added. Major ideas are connected directly to the central concept, and other ideas branch out from those major ideas.

Mind maps can also be drawn by hand, either as "rough notes" during a lecture, meeting or planning session, for example, or as higher quality pictures when more time is available. Mind maps are considered to be a type of spider diagram. A similar concept in the 1970s was "idea sun bursting".


OpenStreetMap (OSM) is a collaborative project to create a free editable map of the world. Rather than the map itself, the data generated by the project is considered its primary output. The creation and growth of OSM has been motivated by restrictions on use or availability of map information across much of the world, and the advent of inexpensive portable satellite navigation devices. OSM is considered a prominent example of volunteered geographic information.

Created by Steve Coast in the UK in 2004, it was inspired by the success of Wikipedia and the predominance of proprietary map data in the UK and elsewhere. Since then, it has grown to over 2 million registered users, who can collect data using manual survey, GPS devices, aerial photography, and other free sources. This crowdsourced data is then made available under the Open Database License. The site is supported by the OpenStreetMap Foundation, a non-profit organisation registered in England and Wales.

The data from OSM is available for use in both traditional applications, like its usage by Facebook, Craigslist, OsmAnd, Geocaching, MapQuest Open, JMP statistical software, and Foursquare to replace Google Maps, and more unusual roles like replacing the default data included with GPS receivers. OpenStreetMap data has been favourably compared with proprietary datasources, although in 2009 data quality varied across the world.

Presidencies and provinces of British India

The Provinces of India, earlier Presidencies of British India and still earlier, Presidency towns, were the administrative divisions of British governance in India. Collectively, they were called British India. In one form or another, they existed between 1612 and 1947, conventionally divided into three historical periods:

Between 1612 and 1757 the East India Company set up "factories" (trading posts) in several locations, mostly in coastal India, with the consent of the Mughal emperors or local rulers. Its rivals were the merchant trading companies of Portugal, Denmark, Holland and France. By the mid-18th century three "Presidency towns": Madras, Bombay and Calcutta, had grown in size.

During the period of Company rule in India, 1757–1858, the Company gradually acquired sovereignty over large parts of India, now called "Presidencies". However, it also increasingly came under British government oversight, in effect sharing sovereignty with the Crown. At the same time it gradually lost its mercantile privileges.

Following the Indian Rebellion of 1857 the Company's remaining powers were transferred to the Crown. In the new British Raj (1858–1947), sovereignty extended to a few new regions, such as Upper Burma. Increasingly, however, unwieldy presidencies were broken up into "Provinces".


Snapchat is a multimedia messaging app used globally, created by Evan Spiegel, Bobby Murphy, and Reggie Brown, former students at Stanford University, and developed by Snap Inc., originally Snapchat Inc.

One of the principal features of Snapchat is that pictures and messages are usually only available for a short time before they become inaccessible to their recipients. The app has evolved from originally focusing on person-to-person photo sharing to presently featuring users' "Stories" of 24 hours of chronological content, along with "Discover", letting brands show ad-supported short-form content.

Snapchat has become notable for representing a new, mobile-first direction for social media, and places significant emphasis on users interacting with virtual stickers and augmented reality objects. As of February 2018, Snapchat has 187 million daily active users.


A symbol is a mark, sign or word that indicates, signifies, or is understood as representing an idea, object, or relationship. Symbols allow people to go beyond what is known or seen by creating linkages between otherwise very different concepts and experiences. All communication (and data processing) is achieved through the use of symbols. Symbols take the form of words, sounds, gestures, ideas or visual images and are used to convey other ideas and beliefs. For example, a red octagon may be a symbol for "STOP". On a map, a blue line might represent a river. Numerals are symbols for numbers. Alphabetic letters may be symbols for sounds. Personal names are symbols representing individuals. A red rose may symbolize love and compassion. The variable 'x', in a mathematical equation, may symbolize the position of a particle in space.

In cartography, an organized collection of symbols forms a legend for a map.

Topographic map

In modern mapping, a topographic map is a type of map characterized by large-scale detail and quantitative representation of relief, usually using contour lines, but historically using a variety of methods. Traditional definitions require a topographic map to show both natural and man-made features. A topographic survey is typically published as a map series, made up of two or more map sheets that combine to form the whole map. A contour line is a line connecting places of equal elevation.

Natural Resources Canada provides this description of topographic maps:These maps depict in detail ground relief (landforms and terrain), drainage (lakes and rivers), forest cover, administrative areas, populated areas, transportation routes and facilities (including roads and railways), and other man-made features.

Other authors define topographic maps by contrasting them with another type of map; they are distinguished from smaller-scale "chorographic maps" that cover large regions, "planimetric maps" that do not show elevations, and "thematic maps" that focus on specific topics.However, in the vernacular and day to day world, the representation of relief (contours) is popularly held to define the genre, such that even small-scale maps showing relief are commonly (and erroneously, in the technical sense) called "topographic".The study or discipline of topography is a much broader field of study, which takes into account all natural and man-made features of terrain.

Tube map

The Tube map (sometimes called the London Underground Map or the TFL Services Map) is a schematic transport map of the lines, stations and services of the London Underground, known colloquially as "the Tube", hence the map's name. The first schematic Tube map was designed by Harry Beck in 1931. Since then, it has been expanded to include more of London's public transport systems, including the Docklands Light Railway, London Overground, TfL Rail, Tramlink and the Emirates Air Line cable car.

As a schematic diagram, it does not show the geographic locations but rather the relative positions of the stations, lines, the stations' connective relations, and fare zones. The basic design concepts have been widely adopted for other such maps around the world, and for maps of other sorts of transport networks and even conceptual schematics.A regularly updated version of the map is available from the official Transport for London website. In 2006, the tube map was voted one of Britain's top 10 design icons which included Concorde, Mini, Supermarine Spitfire, K2 telephone box, World Wide Web and the AEC Routemaster bus.

United States Geological Survey

The United States Geological Survey (USGS, formerly simply Geological Survey) is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, and the natural hazards that threaten it. The organization has four major science disciplines, concerning biology, geography, geology, and hydrology. The USGS is a fact-finding research organization with no regulatory responsibility.

The USGS is a bureau of the United States Department of the Interior; it is that department's sole scientific agency. The USGS employs approximately 8,670 people and is headquartered in Reston, Virginia. The USGS also has major offices near Lakewood, Colorado, at the Denver Federal Center, and Menlo Park, California.

The current motto of the USGS, in use since August 1997, is "science for a changing world." The agency's previous slogan, adopted on the occasion of its hundredth anniversary, was "Earth Science in the Public Service."

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