A topographical survey is a way to determine the configuration of the earth’s surface. It generally concerns the relief of the earth (or moon, planet or asteroid), which can also include natural and artificial feature such as valley, depressions, streams, dams, bridges and buildings. The recording of terrain involves determining the terrestrial or three-dimensional space position of points and the distances and angles between them. A graphic representation of the relief of an area is called a topographic map, which will be constructed from data which shows the horizontal and vertical locations plotted in the survey. Digital surface models and digital terrain models can show the 3D representation of the results of a topographical survey, with or without objects such as plants or buildings.
A topographical survey is a form of land surveying which measures the elevation of plots on a particular piece of land, which are then presented as contour lines on a plot. A direct topographical survey will accurately determine the relief using the positions of certain points, and find the distances and angles between them. This is done using levelling instruments such as astheodolites, dumpy levels and clinometers. Direct surveys such as these can be manual or GIS-based, the latter being a computerised system used to capture, store, manipulate, analyse, manage and present the findings of the topographical survey.
A topographical survey may be conducted for a number of reasons. The purpose is to determine points in a horizontal coordinate system such as latitude, longitude and altitude. This might be commissioned by architects and engineers before planning the construction of a building or its drainage. Topographical surveys are also carried out for other reasons such as archaeological digs, military planning and geological exploration and mapping.
There are other types of topological survey than a direct survey. Some studies are carried out at a distance from the subject area, called remote sensing. Aerial and satellite imagery are usually a form of remote sensing, and a part of geovisualisation. Aerial and satellite imagery use a non-visual spectra of light to determine the lie of the land, showing vegetation and other land use information in a more detailed way. Photogammetry can be used to survey a 3D surface by using a number of photographic images taken from different positions, usually from different passes of an aerial flight.
Radar and sonar are used to generate Digital Elevation Models. Sonar maps which determine the terrain of the ocean floor are an example of these topographical surveys in use. Another technique of topography is a light detection technique which uses a laser.
Topography is also used in medical practice, for brain mapping, measuring the curvature of conea, and superficial human anatomy. It is also used in mathematics when measuring the variables in a map or space.