Topography ("topo-", "place", and "graphia", "writing") is the study of
Earth's surfacefeatures 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 historyand culture. This meaning is less common in America, where topographic maps with elevationcontours have made "topography" synonymous with relief. The older sense of topography as the study of placestill 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 mapby a variety of techniques, including contour lines, Hypsometric tints, and relief shading. [ [http://www.michigan.gov/cgi/0,1607,7-158-14767-31893--F,00.html "What is topography?"] - Center for Geographic Information] [Definition from WordNet Search - princeton.edu] [Definition from Federal Citizen Information Center - pueblo.gsa.gov]
topographyoriginated in ancient Greeceand continued in ancient Rome, as the detailed description of a place. The word comes from the Greek words Polytonic|τόπος ("topos", place) and Polytonic|γραφία ("graphia", writing). [ [http://www.etymonline.com/index.php?term=topography Online Etymology Dictionary] - etymonline.com] In classical literature this refers to writing about a place or places, what is now largely called ' local history'. In Britain and in Europe in general, the word topography is still sometimes used in its original sense [For example, see the website of the [http://www.topsoc.org London Topographical Society] ] .
Detailed military surveys in Britain (beginning in the late eighteenth century) were called
Ordnance Surveys, and this term was used into the 20th century as generic for topographic surveys and maps [ Oxford English Dictionary "Ordnance Survey"] . The earliest scientific surveys in France were called the Cassinimaps after the family who produced them over four generations [ http://fr.wikipedia.org/wiki/Cartographie#Histoire#France ] . The term "topographic surveys" appears to be American in origin. The earliest detailed surveys in the United States were made by the “Topographical Bureau of the Army,” formed during the War of 1812[ [http://www.topogs.org/History.htm Topographical Engineers - History and Personnel ] ] . After the work of national mapping was assumed by the U.S. Geological Surveyin 1878, the term topographical remained as a general term for detailed surveys and mapping programs, and has been adopted by most other nations as standard.
In the 20th century, the term topography started to be used to describe surface description in other fields where
mappingin a broader sense is used, particularly in medical fields such as neurology.
The objective of topography is to determine the position of any feature or more generally any point in terms of both a horizontal
Coordinate systemsuch as latitude and longitude, and altitude. Identifying (naming) features and recognizing typical landform patterns are also part of the field.
A topographic study may be made for a variety of reasons: military planning and geological exploration have been primary motivators to start survey programs, but detailed information about
terrainand surface features is essential for the planningand constructionof any major civil engineering, public works, or reclamationprojects.
Techniques of topography
There are a variety of approaches to studying topograpy. Which method(s) to use depend on the scale and size of the area under study, its accessibility, and the quality of existing surveys.
Surveying helps determine accurately the terrestrial or
three-dimensional space positionof points and the distances and angles between them using leveling instruments such as theodolites, dumpy levels and clinometers.
Even though remote sensing has greatly speeded up the process of gathering information, and has allowed greater accuracy control over long distances, the direct survey still provides the basic control points and framework for all topographic work, whether manual or
In areas where there has been an extensive direct survey and mapping program (most of Europe and the Continental US, for example), the compiled data forms the basis of basic digital elevation datasets such as
USGS DEMdata. This data must often be "cleaned" to eliminate discrepancies between surveys, but it still forms a valuable set of information for large-scale analysis.
The original American topographic surveys (or the British "Ordnance" surveys) involved not only recording of relief, but identification of landmark features and vegetative land cover.
Remote sensingis a general term for geodata collection at a distance from the subject area.
Aerial and satellite imagery
Besides their role in photogrammetry, aerial and satellite imagery can be used to identify and delineate terrain features and more general land-cover features. Certainly they have become more and more a part of
geovisualization, whether mapsor GISsystems. False-color and non-visible spectraimaging can also help determine the lie of the land by delineating vegetation and other land-use information more clearly. Images can be in visible colours and in other spectra.
Photogrammetry is a measurement technique for which the
co-ordinatesof the points in 3D of an object are determined by the measurements made in two photographic images (or more) taken starting from different positions, usually from different passes of an aerial photography flight. In this technique, the common points are identified on each image. A line of sight (or ray) can be built from the camera location to the point on the object. It is the intersection of its rays ( triangulation) which determines the relative three-dimensional position of the point. Known control points can be used to give these relative positions absolute values. More sophisticated algorithms can exploit other information on the scene known a priori (for example, symmetries in certain cases allowing the rebuilding of three-dimensional co-ordinates starting from one only position of the camera).
Radar and sonar
radarmapping is one of the major techniques of generating Digital Elevation Models (see below). Similar techniques are applied in bathymetric surveys using sonarto determine the terrain of the ocean floor. In recent years, LIDAR(Light Detection and Ranging), a remote sensing technique using a laser instead of radio waves, has increasingly been employed for complex mapping needs such as charting canopies and monitoring glaciers.
Forms of topographic data
Terrain is commonly modelled either using vector (
triangulated irregular networkor TIN) or gridded ( Raster image) mathematical models. In the most applications in environmental sciences, land surface is represented and modelled using gridded models. In civil engineering and entertainment businesses, the most representations of land surface employ some variant of TIN models. In geostatistics, land surface is commonly modelled as a combination of the two signals - the smooth (spatially correlated) and the rough (noise) signal.
In practice, surveyors first sample heights in an area, then use these to produce a Digital Surface Model (also known as a
digital elevation model). The DLSM can then be used to visualize terrain, drape remote sensing images, quantify ecological properties of a surface or extract land surface objects. Note that the contour data or any other sampled elevation datasets are not a DLSM. A DLSM implies that elevation is available continuously at each location in the study area, i.e. that the map represents a complete surface. Digital Land Surface Models should not be confused with Digital Surface Models, which can be surfaces of the canopy, buildings and similar objects. For example, in the case of surface models produces using the LIDARtechnology, one can have several surfaces - starting from the top of the canopy to the actual solid earth. The difference between the two surface models can then be used to derive volumetric measures (height of trees etc).
Raw survey data
Topographic survey information is historically based upon the notes of surveyors. They may derive naming and cultural information from other local sources (for example, boundary delineation may be derived from local
cadastralmapping. While of historical interest, these field notes inherently include errors and contradictions that later stages in map production resolve.
Remote sensing data
As with field notes, remote sensing data (aerial and satellite photography, for example), is raw and uninterpreted. It may contain holes (due to cloud cover for example) or inconsistencies (due to the timing of specific image captures). Most modern topographic mapping includes a large component of remotely sensed data in its compilation process.
In its contemporary definition, topographic mapping shows relief. In the United States,
USGStopographic maps show relief using contour lines. The USGS calls maps based on topographic surveys, but without contours, "planimetric maps."
These maps show not only the contours, but also any significant streams or other bodies of
water, forestcover, built-up areas or individual buildings (depending on scale), and other features and points of interest.
While not officially "topographic" maps, the national surveys of other nations share many of the same features, and so they are often generally called "topographic maps."
Existing topographic survey maps, because of their comprehensive and encyclopedic coverage, form the basis for much derived topographic work. Digital Elevation Models, for example, have often been created not from new remote sensing data but from existing paper topographic maps. Many government and private publishers use the artwork (especially the contour lines) from existing topographic map sheets as the basis for their own specialized or updated topographic maps [ see for example the publications of [http://www.ngmapstore.com/jump.jsp?itemType=CATEGORY&itemID=54 National Geographic Trails Illustrated Maps] and
Topographic mapping should not be confused with
Geologic mapping. The latter is concerned with underlying structures and processes to the surface, rather than with identifiable surface features.
Digital elevation modeling
The digital elevation model (DEM) is a
raster-based digitaldataset of the topography (hypsometry and/or bathymetry) of all or part of the Earth (or a telluric planet). The pixelsof the dataset are each assigned an elevation value, and a header portion of the dataset defines the area of coverage, the units each pixel covers, and the units of elevation (and the zero-point). DEMs may be derived from existing paper maps and survey data, or they may be generated from new satellite or other remotely-sensed radaror sonardata.
geographic information system(GIS) can recognize and analyze the spatial relationships that exist within digitally stored spatial data. These topological relationships allow complex spatial modelling and analysis to be performed. Topological relationships between geometric entities traditionally include adjacency (what adjoins what), containment (what encloses what), and proximity (how close something is to something else).
* reconstitute a sight in synthesized images of the ground,
* determine a trajectory of overflight of the ground,
* calculate surfaces or volumes,
* trace topographic profiles,
Topography in other fields
Topography has been applied to different science fields. In
neuroscience, the neuroimagingdiscipline uses techniques such as EEG topographyfor brain mapping. In ophthalmology, corneal topographyis used as a technique for mapping the surface curvature of the cornea.
human anatomy, topography is superficial human anatomy.
Topography as the study of place
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Topography — To*pog ra*phy, n. [F. topographie, Gr. ?; ? a place + ? to write.] The description of a particular place, town, manor, parish, or tract of land; especially, the exact and scientific delineation and description in minute detail of any place or… … The Collaborative International Dictionary of English
topography — (n.) early 15c., from L.L. topographia, from Gk. topographia a description of a place, from topographos describing a place (as a noun, one who is skilled in topography ), from topos place + graphein to write (see GRAPHY (Cf. graphy)) … Etymology dictionary
topography — [tə päg′rə fē] n. pl. topographies [ME topographye < LL topographia < Gr: see TOPIC & GRAPHY] 1. the accurate and detailed description of a place 2. a) the science of drawing on maps and charts or otherwise representing the surface features … English World dictionary
topography — ► NOUN 1) the arrangement of the natural and artificial physical features of an area. 2) a detailed description or representation on a map of such features. DERIVATIVES topographer noun topographic adjective topographical adjective. ORIGIN from… … English terms dictionary
topography — [[t]təpɒ̱grəfi[/t]] topographies 1) N UNCOUNT Topography is the study and description of the physical features of an area, for example its hills, valleys, or rivers, or the representation of these features on maps. 2) N COUNT: usu sing, with poss … English dictionary
topography — UK [təˈpɒɡrəfɪ] / US [təˈpɑɡrəfɪ] noun Word forms topography : singular topography plural topographies 1) [uncountable] the study of the features of land, for example hills, rivers, and roads, and the process of making maps 2)… … English dictionary
topography — The configuration of the ground to include its relief and all features. Topography addresses both dry land and the sea floor (underwater topography) … Military dictionary
topography — noun Etymology: Middle English topographie, from Late Latin topographia, from Greek, from topographein to describe a place, from topos place + graphein to write more at carve Date: 15th century 1. a. the art or practice of graphic delineation in… … New Collegiate Dictionary
topography — In anatomy, the description of any part of the body, especially in relation to a definite and limited area of the surface. [topo + G. graphe, a writing] * * * to·pog·ra·phy tə päg rə fē n, pl phies 1) the physical or natural features of … Medical dictionary
topography — to|pog|ra|phy [ tə pagrəfi ] noun 1. ) count or uncount the features of a particular area of land: the topography of Mars 2. ) uncount the study of the features of land, for example hills, rivers, and roads, and the process of making maps ╾… … Usage of the words and phrases in modern English