Topography

Topographic map of Iran.

Topographic map of the department of Flores, Uruguay.

The topography is the science that studies the set of principles and procedures that aim to graphically represent the earth, with its shapes and details; both natural and artificial; (see planimetry and altimetry). This representation takes place on flat surfaces, limited to small extensions of land, using the denomination of "geodesy" for larger areas. In a very simple way, it can be said that for a surveyor the Earth is flat (geometrically), while for geodesy it is not.

For this, a three-dimensional coordinate system is used, being the x and the y competence of the planimetry, and the z of the altimetry.

The topographic maps use the system of representation of bounded planes, showing the elevation of the land using lines that connect the points with the same elevation with respect to a reference plane, called contour lines, in which case it is said that the map it is hypsographic. Said reference plane can be sea level, and if it is, it will be referred to as altitudes instead of heights.

Field of action

The topography is essential in various fields; For example:

• Agrimensura
• Archaeology
• Architecture
• Geography
• Geology
• Mine engineering
• Geological Engineering
• Geographical Engineering
• Catastral and Geodetic Engineering
• Forestry Engineering
• Agricultural Engineering
• Civil engineering
• Mechatronic Engineering
• Health engineering
• Mining
• Geographic Information Systems
• Batimetrics
• Oceanography
• Cartography
• Sewerage
• Road design
• Tunnels
• Petrolera Engineering
• Environmental Engineering
• Engineering in Transport and Communication routes
• Fisheries engineering
• Agronomy
• Speleology
• Geomatic engineering

Topographic work

Topography is a geometric science applied to the description of the surrounding immobile physical reality. It is to capture in a topographic plane the reality seen in the field, in the rural or natural environment, of the terrestrial surface; In the urban environment, it is the description of the existing facts in a certain place: walls, buildings, streets, among others.

Survey work can be divided into two congruent activities: bringing “the terrain to the cabinet” (by measuring points or revealing it, filing it on the electronic instrument, and then editing it on the computer) and bringing “the cabinet to the terrain” (by staking the reverse path, from a project on the computer to its location using points on the ground). The surveyed or staked points have a three-dimensional value; that is, the location of each point is determined in the horizontal plane (of two dimensions, north and east) and in height (third dimension).

Topography is not only limited to carrying out field surveys in the field, but also has editing and cartographic writing components, so that when making a plan, the phoneme represented can be understood through the use of conventional and standard symbols, previously standards for the representation of natural and anthropic objects on maps or topographic charts. It is also used in mining engineering.

Civil works: buildings, bridges, roads, etc.

The task of the surveyor is prior to and/or during a project: an architect or engineer must have a good prior plan-millimeter or three-dimensional survey of the terrain and of "existing facts" (immobile and fixed elements to the ground) either that the work is built in rural or urban areas.

Carried out the project based on this revelation, the surveyor is in charge of "rethinking" it: he locates the limits of the work, the axes from which the elements are measured (walls, pillars...); sets the reference levels or height.

During the work, at any time, the foreman can request a "status of work" (a disclosure in situation to verify if it is being built within the precision established by the specifications) to the surveyor. The precision of a work varies: a nuclear power plant is not the same as the location of the axis of an irrigation canal, for example.

Measurements

• In agrimensura elements such as measuring tape, podometer, groaning squad, or even the number of steps from one point to another are used.
• In classic topography, to give coordinates of a point, a three-dimensional cartesian system is not directly used, but a system of spherical or polar coordinates is used which later allows us to obtain Cartesian coordinates. For this we need to know two angles and a distance.

We distinguish two types of measurement:

• The direct: that is enough to compare the distance to measure with the unit, (a metric tape above a table, for example)
• The indirect: in which we will need a formula to obtain the measurement.

There are various instruments that can measure angles, such as the total station. For the measurement of distances we have two methods: stadiametric distances or electronic distancemetry, the latter being more precise. For the first case we will use a tachymeter and for the second the total station. Normally the use of GPS is combined with the total station.

It is mandatory to work in the appropriate Geodetic Reference System, currently ETRS89 in the Peninsula and the Balearic Islands and REGCAN95 in the Canary Islands. The reference ellipsoid will be the GRS80 and the corresponding Cartographic Projection is the UTM.

Data collection

Currently the most widely used method for data collection is based on the use of a total station, with which horizontal angles, vertical angles and distances can be measured. Knowing the coordinates of the place where the Station has been placed, it is possible to determine the three-dimensional coordinates of all the points that are measured.

By subsequently processing the coordinates of the data collected, it is possible to draw and graphically represent the details of the terrain considered. With the coordinates of two points it is also possible to calculate the distances or the difference in level between the same points even if you had not parked at any.

In topography, it is considered the inverse process to staking out, since by means of data collection the details of the current terrain are drawn on plans. This method is being replaced by the use of GPS, although it will always be present since there is not always coverage in the GPS receiver due to various factors (example: inside a tunnel). The use of GPS considerably reduces the work, being able to achieve good precisions of 2 to 3 cm if working kinematically and even 2 mm statically.^{[citation required]} The altimetry or z data collected by the station are not and should not be taken as definitive until they are verified by differential leveling.

Stakeout

Stakeout is the reverse process of data collection, and consists of capturing on the ground details represented in plans, such as the place to place foundation axes, previously drawn in plans. The setting out, like the alignment, is an important part of topography. Both are a fundamental previous step to be able to proceed with the realization of the work.

Axes of setting out

The axes needed to perform the stakeout are:

• Horizontal Axis
• Vertical
• Axis of cotas
• Rotationaxis

History of topography

The exact origin of the topography is currently unknown. It is believed that the first topographical works were done in Egypt, since there are representations on walls and tablets. In 1400 B.C. C. Herodotus tells Seostris, to divide the lands of Egypt into properties to collect taxes, creating civil servant positions called "rope sellers" who are dedicated to measuring.

In Egypt, in each arable land, a portion was allocated to Pharaoh, which was marked by a border. With the flooding of the Nile, these boundaries were erased, so that each year the exact amount that corresponded to Pharaoh was marked again. Pharaoh's surveyors were in charge of this task. The instructions of Amenempe, at the end of the 19th dynasty (12th century BC) as transcribed by the scribe, lists the tasks of the chief surveyor "the grain supervisor who controls the measure, who sets the harvest quotas for his lord, who registers the isles of new land, in the great name of His Majesty, who registers the marks on the boundaries of the fields, who acts for the king in his enumeration of taxes, who makes the land register of Egypt.".

Other authors mark Thales of Miletus and Anaximander as the beginning of topography, who are the ones who made the first geographical maps.

As the French geographer engineer P. Merlin points out, “topography was born at the same time as private property”.

Topography, as a science, has been improving according to the technological evolution of each era.