View source for Topography

{{Short description|Study of the forms of land surfaces}}
{{Distinguish|Topology|Typography|Tomography}}
{{About|the study of Earth's surface shape and features|discussion of land surfaces themselves|Terrain|other uses}}
{{More citations needed|date=January 2021}}
[[File:Topographic map example.png|thumb|upright=1.3|A topographic map of [[Stowe, Vermont]] with [[contour line]]s]]
[[File:Aster newyorkcity lrg.jpg|thumb|upright|This [[false color|false-color]] [[satellite imagery|satellite image]] illustrates topography of the [[Urban area#United States|urban core]] of the [[New York metropolitan area]], with [[Manhattan]] at its center.]]

'''Topography''' is the study of forms and features of [[land surface]]s. The topography of an area may refer to landforms and features themselves, or a description or [[depiction]] in maps.

Topography is a field of [[geoscience]] and [[planetary science]], and is concerned with local detail in general, including not only [[Terrain#Relief|relief]], but also [[natural environment|natural]], artificial, and [[culture|cultural]] features such as roads, land boundaries, and buildings.<ref>{{Cite book |last1=West |first1=Terry R. |title=Geology Applied to Engineering |last2=Shakoor |first2=Abdul |date=2018-03-19 |publisher=Waveland Press |isbn=978-1-4786-3722-6 |edition=2nd |pages=[https://books.google.com/books?id=vRRSDwAAQBAJ&dq=topography+includes+cultural+features&pg=PA545 545] |language=en}}</ref> In the United States, topography often means specifically relief, even though the [[United States Geological Survey|USGS]] [[Quadrangle (geography)|topographic maps]] record not just [[elevation]] contours, but also roads, populated places, structures, land boundaries, and so on.<ref>{{Cite web |date=October 2013 |title=US Topo—Topographic Maps for the Nation |url=https://pubs.usgs.gov/fs/2013/3093/pdf/fs2013-3093.pdf |publisher=United States Geological Survey}}</ref>

Topography in a narrow sense involves the recording of relief or [[terrain]], the three-dimensional quality of the surface, and the identification of specific [[landform]]s; this is also known as [[geomorphometry]]. In modern usage, this involves generation of elevation data in digital form ([[Digital Elevation Model|DEM]]). It is often considered to include the graphic representation of the landform on a [[map]] by a variety of [[cartographic relief depiction]] techniques, including [[contour line]]s, [[hypsometric tints]], and [[Shaded relief|relief shading]].

==Etymology==
{{See also|Topographic map#History}}

The term ''topography'' originated in [[ancient Greece]] and continued in [[ancient Rome]], as the detailed description of a place. The word comes from the [[Ancient Greek|Greek]] {{Lang|grc|τόπος}} (''topos'', "place") and {{Lang|grc|-γραφία}} (''-graphia'', "writing").<ref>[http://www.etymonline.com/index.php?term=topography Online Etymology Dictionary] – etymonline.com</ref> 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.<ref>For example, see the websites of the [https://www.victoriacountyhistory.ac.uk/explore/themes/settlement-and-topography Victoria County History] and [https://www.topsoclondon.org/ London Topographical Society]</ref>

Detailed military surveys in [[Great Britain|Britain]] (beginning in the late eighteenth century) were called [[Ordnance Survey]]s, and this term was used into the 20th century as generic for topographic surveys and maps.<ref>''[[Oxford English Dictionary]]'' – "Ordnance Survey"</ref> The earliest scientific surveys in France were the [[French cartography#Cassini maps|Cassini maps]] after the family who produced them over four generations.<ref>{{cite web |last1=Baena |first1=Victoria |title=Revolutionary Cartography and the Cassini Map of France |url=https://www.nypl.org/blog/2022/10/18/revolutionary-cartography-and-cassini-map-france |website=New York Public Library |access-date=16 June 2024}}</ref> 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]],<ref>[http://www.topogs.org/History.htm Topographical Engineers – History and Personnel<!-- Bot generated title -->] {{Webarchive|url=https://web.archive.org/web/20140926122419/http://www.topogs.org/History.htm |date=2014-09-26 }}</ref> which became the [[Corps of Topographical Engineers]] in 1838.<ref>''Charting the Inland Seas: A History of the U.S. Lake Survey'', Arthur M. Woodford, 1991</ref> After the work of national mapping was assumed by the [[United States Geological Survey]] in 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 [[map]]ping in a broader sense is used, particularly in medical fields such as [[neurology]].

==Objectives==
An objective of topography is to determine the position of any feature or more generally any point in terms of both a horizontal [[coordinate system]] such as latitude, longitude, and [[altitude]]. Identifying (naming) features, and recognizing typical landform patterns are also part of the field.

A [[Surveying|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 [[terrain]] and surface features is essential for the [[planning]] and [[construction]] of any major [[civil engineering]], [[public works]], or [[Land reclamation|reclamation]] projects.

==Techniques==
There are a variety of approaches to studying topography. Which method(s) to use depends on the scale and size of the area under study, its accessibility, and the quality of existing surveys.

===Field survey===
{{Further|Surveying|Geodesy}}[[File:Vermessungspunkt.jpg|thumb|upright=0.7|right|A surveying point in [[Germany]]]]Surveying helps determine accurately the terrestrial or [[three-dimensional space]] position of points and the distances and [[angle]]s between them using [[leveling instrument]]s such as [[theodolite]]s, [[dumpy level]]s and [[clinometer]]s.
[[GPS]] and other [[global navigation satellite systems]] (GNSS) are also used.

Work on one of the first topographic maps was begun in France by [[Giovanni Domenico Cassini]], the great Italian astronomer.

Even though remote sensing has greatly sped 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 [[GIS]]-based.

In areas where there has been an extensive direct survey and mapping program (most of Europe and the Continental U.S., for example), the compiled data forms the basis of basic digital elevation datasets such as [[USGS DEM]] data. 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 [[Topographical surveys|topographic surveys]] (or the British "Ordnance" surveys) involved not only recording of relief, but identification of landmark features and vegetative land cover.

===Remote sensing===
{{Main|Remote sensing}}
[[Remote sensing]] is a general term for geodata collection at a distance from the subject area.

==== '''Use of laser scanners''' ====
[[Lidar|Topographic]] surveys using laser scanners, commonly known as [[lidar]] ('''LI'''ght '''D'''etection '''A'''nd '''R'''anging), is a method for capturing high-resolution spatial data of landscapes, architectural structures, and terrains with a vertical accuracy of 10 centimeters. These surveys utilise a laser scanner that emits millions of laser pulses every second. The travel time of these pulses as they are reflected or bounce back from the ground are measured, allowing for the creation of a detailed point cloud that represents the scanned environment.<ref>{{Cite web |date=2025-01-24 |title=What is Lidar data and where can I download it? {{!}} U.S. Geological Survey |url=https://www.usgs.gov/faqs/what-lidar-data-and-where-can-i-download-it |access-date=2025-10-24 |website=www.usgs.gov |language=en}}</ref><ref>{{Cite web |last=US Department of Commerce |first=National Oceanic and Atmospheric Administration |title=What is LIDAR |url=https://oceanservice.noaa.gov/facts/lidar.html |access-date=2025-10-24 |website=oceanservice.noaa.gov |language=EN-US}}</ref> Products of lidar include [[Digital elevation model|Digital elevation models]] (DEMs), which are a representation of the bare earth topographic surface (excluding vegetation, buildings and other surface objects).<ref>{{Cite web |date=2018-11-07 |title=What is a digital elevation model (DEM)? {{!}} U.S. Geological Survey |url=https://www.usgs.gov/faqs/what-a-digital-elevation-model-dem |access-date=2025-10-24 |website=www.usgs.gov |language=en}}</ref>

====Passive sensor methodologies====
{{Main|Aerial photography|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 [[map]]s or [[GIS]] systems. False-color and non-visible [[spectrum|spectra]] imaging 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 spectrum.

====Photogrammetry====
{{Main|Photogrammetry}}
Photogrammetry is a measurement technique for which the [[co-ordinates]] of the points in [[Three-dimensional space|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 (optics)|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 [[algorithm]]s 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).

====Active sensor methodologies====
Satellite [[RADAR]] mapping is one of the major techniques of generating Digital Elevation Models (see below). Similar techniques are applied in [[bathymetry|bathymetric]] surveys using [[sonar]] to determine the terrain of the ocean floor. In recent years, lidar, a remote sensing technique that uses 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 network]] or TIN) or gridded ([[raster image]]) mathematical models. In the most applications in [[environmental science]]s, 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 [[Soil-surface roughness|rough]] (noise) signal.

In practice, surveyors first sample heights in an area, then use these to produce a Digital Land Surface Model in the form of a [[Triangulated irregular network|TIN]]. The DLSM can then be used to visualize terrain, drape remote sensing images, quantify ecological properties of a surface or extract land surface objects. 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 lidar technology, 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 (topology)|boundary]] delineation may be derived from local [[cadastral]] mapping). 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.

===Topographic mapping===
{{Main|Topographic map}}
[[File:Europe topography map.png|thumb|A map of [[Europe]] using elevation modeling]]
In its contemporary definition, topographic mapping shows relief. In the United States, [[USGS]] topographic 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, [[forest cover]], 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 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.<ref>See for example the publications of [http://www.ngmapstore.com/jump.jsp?itemType=CATEGORY&itemID=54 National Geographic Trails Illustrated Maps] {{Webarchive|url=https://web.archive.org/web/20061116063243/http://www.ngmapstore.com/jump.jsp?itemID=54&itemType=CATEGORY |date=2006-11-16 }} and [[DeLorme]] products.</ref>

Topographic mapping should not be confused with [[geological map]]ping. The latter is concerned with underlying structures and processes to the surface, rather than with identifiable surface features.

===Digital elevation modeling===
{{Main|Digital elevation model}}
[[File:Maps-for-free Sierra Nevada.png|thumb|Relief map: [[Sierra Nevada (Spain)|Sierra Nevada Mountains]], [[Spain]] ]]
[[File:Mtm-05277e 3d.png|thumb|3D rendering of a [[Digital elevation model|DEM]] used for the [[topography of Mars]]]]
The digital elevation model (DEM) is a [[raster graphics|raster]]-based [[Digital data|digital]] dataset of the topography ([[hypsometry]] and/or [[bathymetry]]) of all or part of the Earth (or a [[telluric planet]]). The [[pixels]] of 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 [[radar]] or [[sonar]] data.

===Topological modeling===
[[File:Earth_dry_elevation.stl|thumb|[[STL (file format)|STL 3D model]] of Earth without liquid water with 20× elevation exaggeration]]
A [[geographic information system]] (GIS) can recognize and analyze the spatial relationships that exist within digitally stored spatial data. These topological relationships allow complex spatial [[Model (abstract)|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==
{{Main|Topography (disambiguation)}}
Topography has been applied to different science fields. In [[neuroscience]], the [[neuroimaging]] discipline uses techniques such as EEG topography for [[brain mapping]]. In [[ophthalmology]], [[corneal topography]] is used as a technique for mapping the surface curvature of the [[cornea]]. In [[tissue engineering]], [[atomic force microscopy]] is used to map [[nanotopography]].

In [[human anatomy]], topography is [[superficial human anatomy]].

In mathematics the concept of topography is used to indicate the patterns or general organization of features on a map or as a term referring to the pattern in which variables (or their values) are distributed in a space.

==Topographers==
{{Main category|Topographers}}{{Incomplete list|date=May 2021}}
'''Topographers''' are experts in topography. They study and describe the surface features of a place or region.

==See also==
* [[Cartography]]
* [[Digital elevation model]]
* [[Fall line (topography)]]
* [[Geomorphology]]
* [[Global Relief Model]]
* [[Hypsography]]
* [[Marine topography]]
* [[Sea-surface topography]]
* [[Topographic map]]
* [[Orography]]

==References==
{{Reflist}}

{{Atlas}}
{{Authority control}}

[[Category:Cartography]]
[[Category:Topography| ]]