| Topography is the study of Earth's surface | | | | There are a variety of approaches to studying |
| features or those of other planets, moons, | | | | topograpy. Which method(s) to use depend on |
| and asteroids. | | | | the scale and size of the area under study, |
| | | | its accessibility, and the quality of |
| In a broader sense, topography is concerned | | | | existing surveys. |
| with local detail in general, including not | | | | |
| only relief but also vegetative and | | | | Direct survey |
| human-made features, and even local history | | | | |
| and culture. This meaning is less common in | | | | Surveying helps determine accurately the |
| America, where topographic maps with | | | | terrestrial or three-dimensional space |
| elevation contours have made "topography" | | | | position of points and the distances and |
| synonymous with relief. The older sense of | | | | angles between them using leveling |
| Topography as the study of place still has | | | | instruments such as theodolites, dumpy levels |
| currency in Europe. | | | | and clinometers. |
| | | | |
| For the purposes of this article, topography | | | | Even though remote sensing has greatly |
| specifically involves the recording of relief | | | | speeded up the process of gathering |
| or terrain, the three-dimensional aspect of | | | | information, and has allowed greater accuracy |
| the surface, and the identification of | | | | control over long distances, the direct |
| specific landforms. This is also known as | | | | survey still provides the basic control |
| geomorphometry. In modern usage, this | | | | points and framework for all topographic |
| involves generation of elevation data in | | | | work, whether manual or GIS-based. |
| electronic form. It is often considered to | | | | |
| include the graphic representation of the | | | | In areas where there has been an extensive |
| landform on a map by a variety of techniques, | | | | direct survey and mapping program (most of |
| including contour lines, Hypsometric tints, | | | | Europe and the Continental US, for example), |
| and relief shading. | | | | the compiled data forms the basis of basic |
| | | | digital elevation datasets such as USGS DEM |
| Etymology | | | | data. This data must often be "cleaned" to |
| | | | eliminate discrepancies between surveys, but |
| The term “topography†originated | | | | it still forms a valuable set of information |
| in Ancient Greece and continued in Ancient | | | | for large-scale analysis. |
| Rome, as the detailed description of a place. | | | | |
| The word comes from the Greek words ????? | | | | The original American topographic surveys (or |
| (topos, place) and ?????? (graphia, writing). | | | | Ordnance surveys) involved not only recording |
| In classical literature this refers to | | | | of relief, but identification of landmark |
| writing about a place or places, what is now | | | | features and vegetative land cover. |
| largely called 'local history'. In Britain | | | | |
| and in Europe in general, the word topography | | | | Remote sensing |
| is still sometimes used in its original | | | | |
| sense. | | | | Remote sensing is a general term for geodata |
| | | | collection at a distance from the subject |
| Detailed military surveys in Britain | | | | area. |
| (beginning in the late eighteenth century | | | | |
| were called Ordnance Surveys, and this term | | | | Aerial and satellite imagery |
| was used into the 20th century as generic for | | | | |
| topographic surveys and maps. The earliest | | | | Besides their role in photogrammetry, aerial |
| scientific surveys in France were called the | | | | and satellite imagery can be used to identify |
| Cassini maps after the family who produced | | | | and delineate terrain features and more |
| them over four generations. The term | | | | general land-cover features. Certainly they |
| "topographic surveys" appears to be American | | | | have become more and more a part of |
| in origin. The earliest detailed surveys in | | | | geovisualization, whether maps or GIS |
| the United States were made by the | | | | systems. False-color and non-visible spectra |
| “Topographical Bureau of the | | | | imaging can also help determine the lie of |
| Army,†formed during the War of 1812 . | | | | the land by delineating vegetation and other |
| After the work of national mapping was | | | | land-use information more clearly. Images can |
| assumed by the U.S. Geological Survey in | | | | be in visible colours and in other spectra. |
| 1878, the term topographical remained as a | | | | |
| general term for detailed surveys and mapping | | | | Photogrammetry |
| programs, and has been adopted by most other | | | | |
| nations as standard. | | | | Photogrammetry is a measurement technique for |
| | | | which the co-ordinates of the points in 3D of |
| In the 20th century, the term topography | | | | an object are determined by the measurements |
| started to be used to describe surface | | | | made in two photographic images (or more) |
| description in other fields where mapping in | | | | taken starting from different positions, |
| a broader sense is used, partcularly in | | | | usually from different passes of an aerial |
| medical fields such as neurology. | | | | photography flight. In this technique, the |
| | | | common points are identified on each image. A |
| Objectives | | | | line of sight (or ray) can be built from the |
| | | | camera location to the point on the object. |
| The objective of topography is to determine | | | | It is the intersection of its rays |
| the position of any feature or more generally | | | | (triangulation) which determines the relative |
| any point in terms of both a horizontal | | | | three-dimensional position of the point. |
| Coordinate system such as latitude and | | | | Known control points can be used to give |
| longitude, and altitude. Identifying (naming) | | | | these relative positions absolute values. |
| features and recognizing typical landform | | | | More sophisticated algorithms can exploit |
| patterns are also part of the field. | | | | other information on the scene known a priori |
| | | | (for example, symmetries in certain cases |
| A topographic study may be made for a variety | | | | allowing the rebuilding of three-dimensional |
| of reasons: military planning and geological | | | | co-ordinates starting from one only position |
| exploration have been primary motivators to | | | | of the camera). |
| start survey programs, but detailed | | | | |
| information about terrain and surface | | | | Radar and sonar |
| features is essential for the planning and | | | | |
| construction of any major civil engineering, | | | | Satellite radar mapping is one of the major |
| public works, or reclamation projects. | | | | techniques of generating Digital Elevation |
| | | | Models (see below). Similar techniques are |
| Techniques of topography | | | | applied in bathymetric surveys using sonar to |
| | | | determine the terrain of the ocean floor. |