What is topograhpy

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