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39-611: The Medway Gap is a topographic feature in Kent , England. It was created when the prehistoric River Medway cut roughly south to north through the line of chalk hills now known as the North Downs ; other rivers such as the Darent and the Stour have similar features. Its past significance as a means of travel is indicated by the prehistoric Medway megaliths in the area. Today

78-831: A Topographical Engineer he on occasion might address the American Association for the Advancement of Science . He probably subscribed to Silliman's American Journal of Science and he was a pillar of the Smithsonian Institution . In all, there were six major expeditions into the Louisiana Purchase, the first being the best known Corps of Discovery led by Lewis and Clark in 1804–1806. A second expedition in 1804 included astronomer and naturalist John Dunbar and prominent Philadelphia chemist William Hunter. This expedition attempted to follow

117-413: A broader sense is used, particularly in medical fields such as neurology . 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 topographic study may be made for

156-589: A narrow sense 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 digital form ( 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 lines , hypsometric tints , and relief shading . The term topography originated in ancient Greece and continued in ancient Rome , as

195-486: 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. Terrain is commonly modelled either using vector ( triangulated irregular network or 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,

234-420: 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

273-405: 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 reclamation projects. There are a variety of approaches to studying topography. Which method(s) to use depends on

312-458: 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 are experts in topography. They study and describe the surface features of a place or region. Corps of Topographical Engineers The U.S. Army Corps of Topographical Engineers

351-413: Is a general term for geodata collection at a distance from the subject area. 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 maps or GIS systems. False-color and non-visible spectra imaging can also help determine

390-527: Is concerned with local detail in general, including not only relief , but also natural , artificial, and cultural features such as roads, land boundaries, and buildings. In the United States, topography often means specifically relief , even though the USGS topographic maps record not just elevation contours, but also roads, populated places, structures, land boundaries, and so on. Topography in

429-460: Is concerned with underlying structures and processes to the surface, rather than with identifiable surface features. The digital elevation model (DEM) is a raster -based 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

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468-525: 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, 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

507-422: Is to something else). 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

546-723: The Medway Valley railway line and the A228 road both run through the valley, connecting Tonbridge, West Malling and the Medway Towns. At the north end of the Medway Gap, the river is crossed by the M2 motorway and High Speed 1 viaducts . The Gap is designated as a Biodiversity Opportunity Area by Kent County Council. It also has the effect of creating local weather patterns, thereby frequently exhibiting opposite conditions to

585-651: The "Topographical Bureau of the Army", formed during the War of 1812 , which became the Corps of Topographical Engineers in 1838. After the work of national mapping was assumed by the U.S. 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 mapping in

624-731: The Arkansas River and Red River. This is better known as the Pike Expedition . Spanish forces arrested Pike and confiscated his papers, but assigned a translator and cartographer to translate Pike's documents. In 1817 Major Stephen H. Long explored the upper Mississippi River, selecting sites for Fort Smith on the Arkansas River and Fort St. Anthony at the confluence of the Minnesota and Mississippi. In 1819, President James Monroe and Secretary of War John C. Calhoun ordered General Henry Atkinson to lead what became known as

663-604: 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 topographic surveys (or the British "Ordnance" surveys) involved not only recording of relief, but identification of landmark features and vegetative land cover. Remote sensing

702-568: The Northern and Northwestern Lakes and preparing and publishing nautical charts and other navigation aids. The Lake Survey published its first charts in 1852. William Goetzmann has written: From the year 1838 down to the Civil War, there existed a small but highly significant branch of the Army called the Corps of Topographical Engineers. ... The Engineers were concerned with recording all of

741-699: The Red River to its source in Texas, then controlled by Spain, but turned back after three months. In April 1806 a second Red River Expedition was led by Captain Richard Sparks and included astronomer and surveyor Thomas Freeman and Peter Custis, a University of Pennsylvania medical student who served as the expedition's botanist. The group of 24 traveled 615 miles up the Red River before being turned back by Spanish authorities. President Thomas Jefferson hoped that this expedition would be nearly as important as

780-562: The United States. The work of the Corps in the West had still broader significance. Since a major part of its work was to assemble scientific information in the form of maps, pictures, statistics, and narrative reports about the West, it contributed importantly to the compilation of scientific knowledge about the interior of the North American continent. The Topographical Engineers were sophisticated men of their time who worked closely with

819-440: The West. They laid out national boundaries and directly promoted the advance of settlement by locating and constructing wagon roads, improving rivers and harbors , even performing experiments for the location of subsurface water in the arid regions. In short, they functioned as a department of public works for the West - and indeed for the whole nation, since the operations of the Corps extended to every state and territory of

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858-669: 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. 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 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

897-455: 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. Topographic mapping should not be confused with geologic mapping . The latter

936-747: 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.). 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 cadastral mapping). While of historical interest, these field notes inherently include errors and contradictions that later stages in map production resolve. As with field notes, remote sensing data (aerial and satellite photography, for example),

975-414: 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

1014-454: 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

1053-573: The detailed description of a place. The word comes from the Greek τόπος ( topos , "place") and -γραφία ( -graphia , "writing"). 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. Detailed military surveys in Britain (beginning in

1092-538: 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

1131-505: The foremost scholars in American and European centers of learning. Scientists and artists of all nationalities accompanied their expeditions as partners and co-workers. The Army Topographer considered himself by schooling and profession as one of a company of savants. By virtue of his West Point training and status he was an engineer, something above the ordinary field officer, whose duties were confined usually to strictly military tasks. As

1170-459: The late eighteenth century) were called Ordnance Surveys , and this term was used into the 20th century as generic for topographic surveys and maps. The earliest scientific surveys in France were the Cassini maps after the family who produced them over four generations. The term "topographic surveys" appears to be American in origin. The earliest detailed surveys in the United States were made by

1209-456: 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 is a measurement technique for which the co-ordinates of 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,

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1248-479: 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 Land Surface Model in the form of a TIN . The DLSM can then be used to visualize terrain, drape remote sensing images, quantify ecological properties of

1287-546: The one led by Lewis and Clark, but the interruption by Spanish authorities prevented this hope from being realized. In 1805–1806, Lieutenant Zebulon Pike was ordered by General James Wilkinson , Governor of the Upper Louisiana Territory, to find the source of the Mississippi River. In 1806–1807, President Jefferson ordered Lieutenant Pike, on another expedition, to find the headwaters of

1326-425: 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 position of points and the distances and angles between them using leveling instruments such as theodolites , dumpy levels and clinometers . GPS and other global navigation satellite systems (GNSS) are also used. Work on one of

1365-462: 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). Satellite RADAR mapping is one of the major techniques of generating Digital Elevation Models (see below). Similar techniques are applied in bathymetric surveys using sonar to determine the terrain of the ocean floor. In recent years, LIDAR ( LI ght D etection A nd R anging),

1404-496: The surrounding countryside. In the borough of Tonbridge and Malling , the "Medway Gap" refers to the group of villages in this area i.e. Aylesford , East Malling , Larkfield and Leybourne . Much of the residential development in this area took place after World War II. Most of these settlements are in the Chatham and Aylesford constituency. Topography Topography is a field of geoscience and planetary science and

1443-470: The western phenomena as accurately as possible, whether main-traveled roads or uncharted wilderness. As Army officers they represented the direct concern of the national government the settling of the West. The Corps of Topographical Engineers was a central institution of Manifest Destiny , and in the years before the Civil War its officers made explorations which resulted in the first scientific mapping of

1482-473: Was a branch of the United States Army authorized on 4 July 1838. It consisted only of officers who were handpicked from West Point and was used for mapping and the design and construction of federal civil works such as lighthouses and other coastal fortifications and navigational routes. Members included such officers as George Meade , John C. Frémont , Thomas J. Cram and Stephen Long . It

1521-735: Was merged with the United States Army Corps of Engineers on 31 March 1863, at which point the Corps of Engineers also assumed the Lakes Survey for the Great Lakes . In the mid-19th century, Corps of Engineers' officers ran Lighthouse Districts in tandem with U.S. Naval officers. In 1841, Congress created the Lake Survey. The Survey, based in Detroit, Mich., was charged with conducting a hydrographical survey of

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