View source for Terrain

{{short description|Dimension and shape of land surfaces}}
{{Other|Terrain (disambiguation)}}
{{Distinguish|Terrane}}
{{More citations needed|date=July 2012}}

[[File:AYool topography 15min.png|thumb|Present-day  [[altimetry]] and [[bathymetry]]. Data from the [[National Geophysical Data Center]]'s [https://web.archive.org/web/19990224061554/http://www.ngdc.noaa.gov/seg/fliers/se-1104.shtml TerrainBase Digital Terrain Model].]]
[[File:Maps-for-free Sierra Nevada.png|thumb|Relief map of [[Sierra Nevada (Spain)|Sierra Nevada]], Spain]]
[[File:Alpine Fault SRTM (vertical).jpg|upright|thumb|A shaded and colored image (i.e. terrain is enhanced) of varied terrain from the [[Shuttle Radar Topography Mission]]. This shows an [[topology|elevation model]] of New Zealand's [[Alpine Fault]], running about {{cvt|500|km|mi}} long. The [[escarpment]] is flanked by a vast chain of hills between the [[fault (geology)|fault]] and the [[mountain]]s of the [[Southern Alps]]. Northeast is towards the top.]]

'''Terrain''' ({{etymology|la|{{wikt-lang|la|terra}}|earth}}), alternatively '''relief''' or '''topographical [[relief]]''', is the [[dimension]] and shape of a given surface of a [[land]]. In [[physical geography]], terrain is the lay of the land. This is usually expressed in terms of the [[elevation]], [[slope]], and orientation of terrain features. Terrain affects surface water flow and distribution. Over a large area, it can affect [[weather]] and [[climate]] patterns. [[Bathymetry]] is the study of underwater relief, while [[hypsometry]] studies terrain relative to [[sea level]].

== Importance ==
The understanding of terrain is critical for many reasons: 
* The terrain of a region largely determines its suitability for human settlement: flatter [[alluvial plain]]s tend to have better farming soils than steeper, rockier uplands.<ref>{{cite journal |last1=Dwevedi |first1=Alka |title=15 - Soil sensors: detailed insight into research updates, significance, and future prospects |date=January 1, 2017 |url=https://www.sciencedirect.com/science/article/pii/B9780128042991000163 |journal=[[New Pesticides and Soil Sensors]] |pages=561–594 |editor-last=Grumezescu |editor-first=Alexandru Mihai |publisher=[[Academic Press]] |language=en |isbn=978-0-12-804299-1 |access-date=October 11, 2022 |last2=Kumar |first2=Promod |last3=Kumar |first3=Pravita |last4=Kumar |first4=Yogendra |last5=Sharma |first5=Yogesh K. |last6=Kayastha |first6=Arvind M.|doi=10.1016/B978-0-12-804299-1.00016-3 |url-access=subscription }}</ref>
* In terms of [[environmental quality]], [[agriculture]], [[hydrology]] and other interdisciplinary sciences;<ref name=baker2011>{{cite book|last1=Baker |first1=N.T. |last2=Capel |first2=P.D. |date=2011 |chapter=Environmental factors that influence the location of crop agriculture in the conterminous United States |title=U.S. Geological Survey Scientific Investigations Report 2011–5108 |publisher=[[U.S. Geological Survey]] |page=72}}</ref> understanding the terrain of an area assists the understanding of [[drainage divide|watershed boundaries]], [[drainage basin|drainage characteristics]],<ref>{{cite book |last=Brush |first=L. M. |date=1961 |title=Drainage basins, channels, and flow characteristics of selected streams in central Pennsylvania |pages=1–44 |work=U.S. Department of the Interior, GEOLOGICAL SURVEY |location=Washington D.C. |publisher=[[U.S. Geological Survey]] |access-date=October 29, 2017 |url=https://pubs.usgs.gov/pp/0282f/report.pdf}}</ref> [[drainage system (geomorphology)|drainage systems]], [[hydrogeology|groundwater systems]], [[drainage|water movement]], and impacts on [[water quality#Environmental water quality|water quality]]. Complex arrays of relief data are used as input parameters for [[hydrology transport model]]s (such as the [[SWMM|Storm Water Management Model]] or [[DSSAM Model]]s) to allow prediction of river [[water pollution|water quality]]. 
* Understanding terrain also supports [[soil conservation]], especially in agriculture. [[Contour ploughing]] is an established practice enabling [[sustainable agriculture]] on sloping land; it is the practice of ploughing along lines of equal elevation instead of up and down a slope.
* Terrain is [[military|militarily]] critical because it determines the ability of armed forces to take and hold areas, and move [[troop]]s and material into and through areas. An [[Military geography#Types of terrain|understanding of terrain]] is basic to both defensive and offensive strategy. The military usage of "terrain" is very broad, encompassing not only landform but land use and land cover, surface transport infrastructure, built structures and [[human geography]], and, by extension under the term [[Human Terrain System|human terrain]], even psychological, cultural, or economic factors.<ref>{{cite web|url=https://irp.fas.org/doddir/dod/jp1_02-april2010.pdf |title=Joint Publication 1-02 |website=Department of Defense Dictionary of Military and Associated Terms |quote=* "compartmentation ... [involves] areas bounded on at least two sides by terrain features such as woods..."<br>* "culture — A feature of the terrain that has been constructed by man. Included are such items as roads, buildings, and canals; boundary lines; and, in a broad sense, all names and legends on a map."<br>* "key terrain — Any locality, or area, the seizure or retention of which affords a marked advantage to either combatant."<br>* "terrain intelligence — Intelligence on the military significance of natural and manmade characteristics of an area."}}</ref>

* Terrain is important in determining [[weather]] patterns. Two areas geographically close to each other may differ radically in [[precipitation]] levels or timing because of elevation differences or a [[rain shadow]] effect.
* Precise knowledge of terrain is vital in [[aviation]], especially for low-flying routes and maneuvers ([[Terrain awareness and warning system|see terrain collision avoidance]]) and airport altitudes. Terrain will also affect range and performance of radars and terrestrial [[radio navigation]] systems. Furthermore, a hilly or mountainous terrain can strongly impact the implementation of a new [[aerodrome]] and the orientation of its runways.

== Relief ==
Relief (or ''local relief'') refers specifically to the quantitative measurement of vertical elevation change in a [[landscape]]. It is the difference between maximum and minimum elevations within a given area, usually of limited extent.<ref>{{cite book |last=Summerfield |first=M.A. |url=https://archive.org/details/globalgeomorphol0000summ |title=Global Geomorphology |date=1991 |publisher=[[Pearson Education|Pearson]] |isbn=9780582301566 |page=537 |url-access=registration}}</ref> A relief can be described qualitatively, such as a "{{visible anchor|low relief|Low relief|Low-relief}}" or "{{visible anchor|high relief|High relief|High-relief}}" [[plain]] or [[Upland and lowland|upland]]. The relief of a landscape can change with the size of the area over which it is measured, making the definition of the scale over which it is measured very important. Because it is related to the slope of surfaces within the area of interest and to the [[Stream gradient|gradient]] of any streams present, the relief of a landscape is a useful metric in the study of the Earth's surface. Relief energy, which may be defined ''[[inter alia]]'' as "the maximum height range in a regular grid",<ref>{{cite book|url=https://books.google.com/books?id=YzBNmiGS-7oC&dq=definition+of+%22relief+energy%22&pg=PA48 |title=African Landscapes: Interdisciplinary Approaches |editor1-first=Michael |editor1-last=Bollig |editor2-first=Olaf |editor2-last=Bubenzer |location=Cologne |publisher=Springer |date=2009 |page=48 |isbn=9780387786827 |via=[[Google Books]]}}</ref> is essentially an indication of the ruggedness or relative height of the terrain.

== Geomorphology ==
{{main|Geomorphology}}
Geomorphology is the long term study of the formation of terrain or topography.<ref>{{Cite web |last=Dziak |first=Mark |date=2023 |title=Geomorphology {{!}} EBSCO Research Starters |url=https://www.ebsco.com/research-starters/geology/geomorphology |access-date=2025-08-21 |website=www.ebsco.com |language=en}}</ref> Terrain is formed by concurrent processes operating on the underlying [[Structural geology#Rock macro-structures|geological structures]] over [[Geologic time scale|geological time]]:
* [[Geology|Geological]] processes: migration of [[tectonic plate]]s, [[Fault (geology)|faulting]] and [[Fold (geology)|folding]], [[mountain formation]], [[volcanic eruptions]], etc.
* Erosional [[erosion#Physical processes|processes]]: [[Glacier#Glacial geology|glacial]], [[fluvial#Fluvial processes|water]], [[Aeolian processes#Wind erosion|wind]], [[weathering#Chemical weathering|chemical]] and gravitational ([[mass wasting|mass movement]]); such as [[landslide]]s, [[downhill creep]], [[Landslide classification#Flows|flows]], [[Slump (geology)|slumps]], and [[Landslide classification#Falls|rock falls]].
* [[Impact event|Extraterrestrial]]: [[meteorite]] [[impact crater|impacts]].

[[Tectonic]] processes such as [[Orogeny|orogenies]] and [[Tectonic uplift|uplifts]] cause land to be elevated, whereas erosional and [[weathering]] processes wear the land away by smoothing and reducing topographic features.<ref>{{cite journal|last1=Strak |first1=V. |last2=Dominguez |first2=S. |last3=Petit |first3=C. |last4=Meyer |first4=B. |last5=Loget |first5=N. |date=2011 |title=Interaction between normal fault slip and erosion on relief evolution; insights from experimental modelling |journal=[[Tectonophysics (journal)|Tectonophysics]] |volume=513 |number=1–4 |pages=1–19 |doi=10.1016/j.tecto.2011.10.005|bibcode=2011Tectp.513....1S |url=https://hal.archives-ouvertes.fr/hal-00646966/file/preprint_Strak_2011.pdf }}</ref> The relationship of [[erosion and tectonics]] rarely (if ever) reaches equilibrium.<ref>{{cite journal |last1=Gasparini |first1=N. |last2=Bras |first2=R. |last3=Whipple |first3=K. |date=2006 |title=Numerical modeling of non–steady-state river profile evolution using a sediment-flux-dependent incision model. Special Paper |journal=[[Geological Society of America]] |volume=398 |pages=127–141 |doi=10.1130/2006.2398(08)}}</ref><ref>{{cite journal|last1=Roe |first1=G. |last2=Stolar |first2=D. |last3=Willett |first3=S. |date=2006 |title=Response of a steady-state critical wedge orogen to changes in climate and tectonic forcing. Special Paper |journal=[[Geological Society of America]] |volume=398 |pages=227–239 |doi=10.1130/2005.2398(13)}}</ref><ref>{{cite journal|last1=Stolar |first1=D. |last2=Willett |first2=S. |last3=Roe |first3=G. |date=2006 |title=Climatic and tectonic forcing of a critical orogen. Special Paper |journal=[[Geological Society of America]] |volume=398 |pages=241–250 |doi=10.1130/2006.2398(14)}}</ref> These processes are also codependent, however the full range of their interactions is still a topic of debate.<ref>{{cite journal|last1=Wobus |first1=C. |last2=Whipple |first2=K. |last3=Kirby |first3=E. |last4=Snyder |first4=N. |last5=Johnson |first5=J. |last6=Spyropolou |first6=K. |last7=Sheehan |first7=D. |date=2006 |title=Tectonics from topography: Procedures, promise, and pitfalls. Special Paper |journal=[[Geological Society of America]] |volume=398 |pages=55–74 |doi=10.1130/2006.2398(04)}}</ref><ref>{{harvp|Hoth|Adam|Kukowski|Oncken|2006|pp=201–225}}; {{harvp|Bonnet|Malavieille|Mosar|2007}}; {{harvp|King|Herman|Guralnik|2016|pp=800–804}}</ref><ref>{{cite web |author=[[University of Cologne]] |title=New insights into the relationship between erosion and tectonics in the Himalayas |website=[[ScienceDaily]] |date=23 August 2016 |url=https://www.sciencedaily.com/releases/2016/08/160823083555.htm}}</ref>

Land surface parameters are quantitative measures of various [[morphometric]] properties of a surface. The most common examples are used to derive [[slope]] or [[Aspect (geography)|aspect]] of a terrain or curvatures at each location. These measures can also be used to derive [[Hydrology|hydrological parameters]] that reflect flow/erosion processes. [[Climate|Climatic]] parameters are based on the modelling of [[solar radiation]] or air flow.

Land surface objects, or [[landform]]s, are definite physical objects (lines, points, areas) that differ from the surrounding objects. The most typical examples airlines of [[Water divide|watershed]]s, [[stream]] patterns, [[ridge]]s, [[Fall line|break-line]]s, [[stream pool|pool]]s or borders of specific landforms.

== Digital terrain model ==
{{excerpt|Digital terrain model}}

== See also ==
{{div col|colwidth=23em}}
* [[GNSS applications#Surveying and mapping|Applications of global navigation satellite systems (GNSS)]]
* [[Cartographic relief depiction]] (2D relief map)
* [[Geographic information system]] (GIS)
* [[Geomorphometry]]
* [[Hypsometry]]
* [[Isostasy]]
* [[Physical terrain model]]
* [[Relief ratio]]
* [[Subterranea (geography)|Subterranea]]
* [[Terrain awareness and warning system]]
* [[Terrane]]
* [[Topography]]
{{div col end}}

== References ==
{{reflist}}

=== Bibliography ===
* {{cite journal |last1=Bonnet |first1=C. |last2=Malavieille |first2=J. |last3=Mosar |first3=J. |date=2007 |title=Interactions between tectonics, erosion, and sedimentation during the recent evolution of the Alpine orogen: Analogue modeling insights |journal=[[Tectonics (journal)|Tectonics]] |volume=26 |number=TC6016 |doi=10.1029/2006TC002048|bibcode=2007Tecto..26.6016B |s2cid=131347609 |url=https://hal.archives-ouvertes.fr/hal-00404424/file/ark%20_67375_WNG-7JRV7H29-M.pdf }}
* {{cite journal |last1=Hoth |first1=S. |last2=Adam |first2=J. |last3=Kukowski |first3=N. |last4=Oncken |first4=O. |date=2006 |title=Influence of erosion on the kinematics of bivergent orogens: Results from scaled sandbox simulations. Special Paper |journal=[[Geological Society of America]] |volume=398 |pages=201–225 |doi=10.1130/2006.2398(12)}}
* {{cite journal |last1=King |first1=G. |last2=Herman |first2=F. |last3=Guralnik |first3=B. |date=2016 |title=Northward migration of the eastern himalayan syntaxis revealed by OSL thermochronometry |journal=[[Science (journal)|Science]] |volume=353 |number=6301 |pages=800–804 |doi=10.1126/science.aaf2637|pmid=27540169 |bibcode=2016Sci...353..800K |s2cid=206647417 }}

== Further reading ==
* [http://geographicalimaginations.com/2014/09/20/boots-on-the-ground/ Boots on the ground]. On military terrain from the perspective of the combat soldier. By [[Derek Gregory]]

== External links ==
* [https://maps.google.com/ Google Maps]
* [http://www.microsoft.com/maps/ Bing Maps]
{{Wiktionary-inline|terrain}}

[[Category:Physical geography]]
[[Category:Topography]]
[[Category:Vertical datums]]