Elevation

The elevation of a geographic location is its height above or below a fixed reference point, most commonly a reference geoid, a mathematical model of the Earth's sea level as an equipotential gravitational surface (see Geodetic datum § Vertical datum). The term elevation is mainly used when referring to points on the Earth's surface, while altitude or geopotential height is used for points above the surface, such as an aircraft in flight or a spacecraft in orbit, and depth is used for points below the surface.

Elevation is not to be confused with the distance from the center of the Earth. Due to the equatorial bulge, the summits of Mount Everest and Chimborazo have, respectively, the largest elevation and the largest geocentric distance.

SanBernardinoMountains8000feetsign
Sign at 8,000 feet (2,438 m) in the San Bernardino Mountains of southern California (2009)
Vertical distances
Vertical distance comparison
Earth elevation histogram 2
Elevation histogram of the Earth's surface, of which approximately 71% is covered with water

Maps and GIS

Topomapcropped
Part of a topographic map of Haleakala (Hawaii), showing elevation.
Satellite image of Cape peninsula
Landsat Image over SRTM Elevation by NASA, showing the Cape Peninsula and Cape of Good Hope, South Africa in the foreground.[1]

GIS or geographic information system is a computer system that allows for visualizing, manipulating, capturing, and storage of data with associated attributes. GIS offers better understanding of patterns and relationships of the landscape at different scales. Tools inside the GIS allow for manipulation of data for spatial analysis or cartography.

Srtm ramp2.world.21600x10800
Heightmap of Earth's surface (including water and ice) in equirectangular projection, normalized as 8-bit grayscale, where lighter values indicate higher elevation.

A topographical map is the main type of map used to depict elevation, often through use of contour lines. In a Geographic Information System (GIS), digital elevation models (DEM) are commonly used to represent the surface (topography) of a place, through a raster (grid) dataset of elevations. Digital terrain models are another way to represent terrain in GIS.

USGS (United States Geologic Survey) is developing a 3D Elevation Program (3DEP) to keep up with growing needs for high quality topographic data. 3DEP is a collection of enhanced elevation data in the form of high quality LiDAR data over the conterminous United States, Hawaii, and the U.S. territories. There are three bare earth DEM layers in 3DEP which are nationally seamless at the resolution of 1/3, 1, and 2 arcseconds.[1]

Global 1-kilometer map

This map is derived from GTOPO30 data that describes the elevation of Earth's terrain at intervals of 30 arcseconds (approximately 1 km). It uses color and shading instead of contour lines to indicate elevation.

N60-90, W150-180 N60-90, W120-150 N60-90, W90-120 N60-90, W60-90 N60-90, W30-60 N60-90, W0-30 N60-90, E0-30 N60-90, E30-60 N60-90, E60-90 N60-90, E90-120 N60-90, E120-150 N60-90, E150-180
N30-60, W150-180 N30-60, W120-150 N30-60, W90-120 N30-60, W60-90 N30-60, W30-60 N30-60, W0-30 N30-60, E0-30 N30-60, E30-60 N30-60, E60-90 N30-60, E90-120 N30-60, E120-150 N30-60, E150-180
N0-30, W150-180 N0-30, W120-150 N0-30, W90-120 N0-30, W60-90 N0-30, W30-60 N0-60, W0-30 N0-60, E0-30 N0-60, E30-60 N0-60, E60-90 N0-60, E90-120 N0-60, E120-150 N0-60, E150-180
S0-30, W150-180 S0-30, W120-150 S0-30, W90-120 S0-30, W60-90 S0-30, W30-60 S0-30, W0-30 S0-30, E0-30 S0-30, E30-60 S0-30, E60-90 S0-30, E90-120 S0-30, E120-150 S0-30, E150-180
S30-60, W150 S30-60, W120 S30-60, W90-120 S30-60, W60-90 S30-60, W30-60 S30-60, W0-30 S30-60, E0-30 S30-60, E30-60 S30-60, E60-90 S30-60, E90-120 S30-60, E120-150 S30-60, E150-180
S60-90, W150-180 S60-90, W120-150 S60-90, W90-120 S60-90, W60-90 S60-90, W30-60 S60-90, W0-30 S60-90, E0-30 S60-90, E30-60 S60-90, E60-90 S60-90, E90-120 S60-90, E120-150 S60-90, E150-180
Each tile is available at a resolution of 1800 × 1800 pixels (approximate file size 1 MB, 60 pixels = 1 degree, 1 pixel = 1 minute)
Airborne Lidar Bathymetric Technology
Processed LiDAR point cloud showing not only elevation, but heights of features as well.

See also

References

  1. ^ Survey, U.S. Geological. "The National Map: Elevation". nationalmap.gov. Retrieved 2017-02-24.

External links

Altitude

Altitude or height (sometimes known as 'depth') is defined based on the context in which it is used (aviation, geometry, geographical survey, sport, atmospheric pressure, and many more). As a general definition, altitude is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The reference datum also often varies according to the context. Although the term altitude is commonly used to mean the height above sea level of a location, in geography the term elevation is often preferred for this usage.

Vertical distance measurements in the "down" direction are commonly referred to as depth.

Anatomical terms of motion

Motion, the process of movement, is described using specific anatomical terms. Motion includes movement of organs, joints, limbs, and specific sections of the body. The terminology used describes this motion according to its direction relative to the anatomical position of the joints. Anatomists use a unified set of terms to describe most of the movements, although other, more specialized terms are necessary for describing the uniqueness of the movements such as those of the hands, feet, and eyes.

In general, motion is classified according to the anatomical plane it occurs in. Flexion and extension are examples of angular motions, in which two axes of a joint are brought closer together or moved further apart. Rotational motion may occur at other joints, for example the shoulder, and are described as internal or external. Other terms, such as elevation and depression, describe movement above or below the horizontal plane. Many anatomical terms derive from Latin terms with the same meaning.

Antarctica

Antarctica (UK: or , US: (listen)) is Earth's southernmost continent. It contains the geographic South Pole and is situated in the Antarctic region of the Southern Hemisphere, almost entirely south of the Antarctic Circle, and is surrounded by the Southern Ocean. At 14,200,000 square kilometres (5,500,000 square miles), it is the fifth-largest continent and nearly twice the size of Australia. At 0.00008 people per square kilometre, it is by far the least densely populated continent. About 98% of Antarctica is covered by ice that averages 1.9 km (1.2 mi; 6,200 ft) in thickness, which extends to all but the northernmost reaches of the Antarctic Peninsula.

Antarctica, on average, is the coldest, driest, and windiest continent, and has the highest average elevation of all the continents. Most of Antarctica is a polar desert, with annual precipitation of 20 cm (7.9 in) along the coast and far less inland. The temperature in Antarctica has reached −89.2 °C (−128.6 °F) (or even −94.7 °C (−135.8 °F) as measured from space), though the average for the third quarter (the coldest part of the year) is −63 °C (−81 °F). Anywhere from 1,000 to 5,000 people reside throughout the year at research stations scattered across the continent. Organisms native to Antarctica include many types of algae, bacteria, fungi, plants, protista, and certain animals, such as mites, nematodes, penguins, seals and tardigrades. Vegetation, where it occurs, is tundra.

Antarctica is noted as the last region on Earth in recorded history to be discovered, unseen until 1820 when the Russian expedition of Fabian Gottlieb von Bellingshausen and Mikhail Lazarev on Vostok and Mirny sighted the Fimbul ice shelf. The continent, however, remained largely neglected for the rest of the 19th century because of its hostile environment, lack of easily accessible resources, and isolation. In 1895, the first confirmed landing was conducted by a team of Norwegians.

Antarctica is a de facto condominium, governed by parties to the Antarctic Treaty System that have consulting status. Twelve countries signed the Antarctic Treaty in 1959, and thirty-eight have signed it since then. The treaty prohibits military activities and mineral mining, prohibits nuclear explosions and nuclear waste disposal, supports scientific research, and protects the continent's ecozone. Ongoing experiments are conducted by more than 4,000 scientists from many nations.

Atmospheric pressure

Atmospheric pressure, sometimes also called barometric pressure (after the sensor), is the pressure within the atmosphere of Earth (or that of another planet). The standard atmosphere (symbol: atm) is a unit of pressure defined as 1013.25 mbar (101325 Pa), equivalent to 760 mm Hg (torr), 29.9212 inches Hg, or 14.696 psi. The atm unit is roughly equivalent to the mean sea-level atmospheric pressure on Earth, that is, the Earth's atmospheric pressure at sea level is approximately 1 atm.

In most circumstances atmospheric pressure is closely approximated by the hydrostatic pressure caused by the weight of air above the measurement point. As elevation increases, there is less overlying atmospheric mass, so that atmospheric pressure decreases with increasing elevation. Pressure measures force per unit area, with SI units of Pascals (1 pascal = 1 newton per square metre, 1 N/m2). On average, a column of air with a cross-sectional area of 1 square centimetre (cm2), measured from mean (average) sea level to the top of Earth's atmosphere, has a mass of about 1.03 kilogram and exerts a force or "weight" of about 10.1 newtons, resulting in a pressure of 10.1 N/cm2 or 101 kN/m2 (101 kilopascals, kPa). A column of air with a cross-sectional area of 1 in2 would have a weight of about 14.7 lbf, resulting in a pressure of 14.7 lbf/in2.

Death Valley

Death Valley is a desert valley located in Eastern California, in the northern Mojave Desert bordering the Great Basin Desert. It is one of the hottest places in the world along with deserts in the Middle East.Death Valley's Badwater Basin is the point of the lowest elevation in North America, at 282 feet (86 m) below sea level. This point is 84.6 miles (136.2 km) east-southeast of Mount Whitney, the highest point in the contiguous United States, with an elevation of 14,505 feet (4,421 m). On the afternoon of July 10, 1913, the United States Weather Bureau recorded a high temperature of 134 °F (56.7 °C) at Furnace Creek in Death Valley. This temperature stands as the highest ambient air temperature ever recorded at the surface of the Earth.Located near the border of California and Nevada, in the Great Basin, east of the Sierra Nevada mountains, Death Valley constitutes much of Death Valley National Park and is the principal feature of the Mojave and Colorado Deserts Biosphere Reserve. It is located mostly in Inyo County, California. It runs from north to south between the Amargosa Range on the east and the Panamint Range on the west; the Grapevine Mountains and the Owlshead Mountains form its northern and southern boundaries, respectively. It has an area of about 3,000 sq mi (7,800 km2). The highest point in Death Valley itself is Telescope Peak in the Panamint Range, which has an elevation of 11,043 feet (3,366 m).

Digital elevation model

A digital elevation model (DEM) is a 3D CG representation of a terrain's surface – commonly of a planet (e.g. Earth), moon, or asteroid – created from a terrain's elevation data. A "global DEM" refers to a Discrete Global Grid.

DEMs are used often in geographic information systems, and are the most common basis for digitally produced relief maps. While a DSM may be useful for landscape modeling, city modeling and visualization applications, a DTM is often required for flood or drainage modeling, land-use studies, geological applications, and other applications, and in planetary science.

Geographic information system

A geographic information system (GIS) is a system designed to capture, store, manipulate, analyze, manage, and present spatial or geographic data. GIS applications are tools that allow users to create interactive queries (user-created searches), analyze spatial information, edit data in maps, and present the results of all these operations. GIS (more commonly GIScience) sometimes refers to geographic information science (GIScience), the science underlying geographic concepts, applications, and systems.GIS can refer to a number of different technologies, processes, techniques and methods. It is attached to many operations and has many applications related to engineering, planning, management, transport/logistics, insurance, telecommunications, and business. For that reason, GIS and location intelligence applications can be the foundation for many location-enabled services that rely on analysis and visualization.

GIS can relate unrelated information by using location as the key index variable. Locations or extents in the Earth space–time may be recorded as dates/times of occurrence, and x, y, and z coordinates representing, longitude, latitude, and elevation, respectively. All Earth-based spatial–temporal location and extent references should be relatable to one another and ultimately to a "real" physical location or extent. This key characteristic of GIS has begun to open new avenues of scientific inquiry.

List of U.S. states and territories by elevation

The elevation of the U.S. states, the federal district, and the territories may be described in several ways. These include:

the elevation of their highest point;

the elevation of their lowest point

and the difference between (range of) their highest points and lowest points.The following list is a comparison of elevation absolutes in the United States. Data include interval measures of highest and lowest elevation for all 50 states, the District of Columbia, and territories.Which state or territory is "highest" and "lowest" is determined by the definition of "high" and "low". For instance, Alaska could be regarded as the highest state because Denali, at 20,310 feet (6,190.5 m), is the highest point in the United States. However, Colorado, with the highest mean elevation of any state as well as the highest low point, could also be considered a candidate for "highest state". Determining which state is "lowest" is equally problematic. California contains the Badwater Basin in Death Valley, at 279 feet (85 m) below sea level, the lowest point in the United States; while Florida has the lowest high point, and Delaware has the lowest mean elevation. Florida is also the flattest state, with the smallest difference between its highest and lowest points.

The list of highest points in each state is important to the sport of highpointing, where enthusiasts attempt to visit the highest point in each of the contiguous 48 states, or in all 50 states, or in all 50 states plus the District of Columbia and the territories. As of 2006, 155 people had reached all fifty state highpoints. Roughly 200–300 people attend the Highpointers Club convention each year.All elevations in the table below have been adjusted to the North American Vertical Datum of 1988. The mean elevation for each state is accurate to the nearest 100 ft (30 m).

Metres above sea level

Metres above mean sea level (MAMSL) or simply metres above sea level (MASL or m a.s.l.) is a standard metric measurement in metres of vertical distance (height, elevation or altitude) of a location in reference to a historic mean sea level taken as a vertical datum. Mean sea levels are affected by climate change and other factors and change over time. For this and other reasons, recorded measurements of elevation above sea level might differ from the actual elevation of a given location over sea level at a given moment.

Montane ecosystems

Montane ecosystems refers to any ecosystem found in mountains. These ecosystems are strongly affected by climate, which gets colder as elevation increases. They are stratified according to elevation. Dense forests are common at moderate elevations. However, as the elevation increases, the climate becomes harsher, and the plant community transitions to grasslands or tundra.

Mount Whitney

Mount Whitney is the tallest mountain in the contiguous United States and the Sierra Nevada, with an elevation of 14,505 feet (4,421 m). It is located in East–Central California, on the boundary between California's Inyo and Tulare counties, 84.6 miles (136.2 km) west-northwest of the lowest point in North America at Badwater Basin in Death Valley National Park at 282 ft (86 m) below sea level. The west slope of the mountain is in Sequoia National Park and the summit is the southern terminus of the John Muir Trail which runs 211.9 mi (341.0 km) from Happy Isles in Yosemite Valley. The east slope is in the Inyo National Forest in Inyo County.

Mountain

A mountain is a large landform that rises above the surrounding land in a limited area, usually in the form of a peak. A mountain is generally steeper than a hill. Mountains are formed through tectonic forces or volcanism. These forces can locally raise the surface of the earth. Mountains erode slowly through the action of rivers, weather conditions, and glaciers. A few mountains are isolated summits, but most occur in huge mountain ranges.

High elevations on mountains produce colder climates than at sea level. These colder climates strongly affect the ecosystems of mountains: different elevations have different plants and animals. Because of the less hospitable terrain and climate, mountains tend to be used less for agriculture and more for resource extraction and recreation, such as mountain climbing.

The highest mountain on Earth is Mount Everest in the Himalayas of Asia, whose summit is 8,850 m (29,035 ft) above mean sea level. The highest known mountain on any planet in the Solar System is Olympus Mons on Mars at 21,171 m (69,459 ft).

Myocardial infarction

Myocardial infarction (MI), also known as a heart attack, occurs when blood flow decreases or stops to a part of the heart, causing damage to the heart muscle. The most common symptom is chest pain or discomfort which may travel into the shoulder, arm, back, neck or jaw. Often it occurs in the center or left side of the chest and lasts for more than a few minutes. The discomfort may occasionally feel like heartburn. Other symptoms may include shortness of breath, nausea, feeling faint, a cold sweat or feeling tired. About 30% of people have atypical symptoms. Women more often present without chest pain and instead have neck pain, arm pain or feel tired. Among those over 75 years old, about 5% have had an MI with little or no history of symptoms. An MI may cause heart failure, an irregular heartbeat, cardiogenic shock or cardiac arrest.Most MIs occur due to coronary artery disease. Risk factors include high blood pressure, smoking, diabetes, lack of exercise, obesity, high blood cholesterol, poor diet and excessive alcohol intake, among others. The complete blockage of a coronary artery caused by a rupture of an atherosclerotic plaque is usually the underlying mechanism of an MI. MIs are less commonly caused by coronary artery spasms, which may be due to cocaine, significant emotional stress and extreme cold, among others. A number of tests are useful to help with diagnosis, including electrocardiograms (ECGs), blood tests and coronary angiography. An ECG, which is a recording of the heart's electrical activity, may confirm an ST elevation MI (STEMI), if ST elevation is present. Commonly used blood tests include troponin and less often creatine kinase MB.Treatment of an MI is time-critical. Aspirin is an appropriate immediate treatment for a suspected MI. Nitroglycerin or opioids may be used to help with chest pain; however, they do not improve overall outcomes. Supplemental oxygen is recommended in those with low oxygen levels or shortness of breath. In a STEMI, treatments attempt to restore blood flow to the heart and include percutaneous coronary intervention (PCI), where the arteries are pushed open and may be stented, or thrombolysis, where the blockage is removed using medications. People who have a non-ST elevation myocardial infarction (NSTEMI) are often managed with the blood thinner heparin, with the additional use of PCI in those at high risk. In people with blockages of multiple coronary arteries and diabetes, coronary artery bypass surgery (CABG) may be recommended rather than angioplasty. After an MI, lifestyle modifications, along with long term treatment with aspirin, beta blockers and statins, are typically recommended.Worldwide, about 15.9 million myocardial infarctions occurred in 2015. More than 3 million people had an ST elevation MI, and more than 4 million had an NSTEMI. STEMIs occur about twice as often in men as women. About one million people have an MI each year in the United States. In the developed world, the risk of death in those who have had an STEMI is about 10%. Rates of MI for a given age have decreased globally between 1990 and 2010. In 2011, a MI was one of the top five most expensive conditions during inpatient hospitalizations in the US, with a cost of about $11.5 billion for 612,000 hospital stays.

Sea level

Mean sea level (MSL) (often shortened to sea level) is an average level of the surface of one or more of Earth's bodies of water from which heights such as elevation may be measured. The global MSL is a type of vertical datum – a standardised geodetic datum – that is used, for example, as a chart datum in cartography and marine navigation, or, in aviation, as the standard sea level at which atmospheric pressure is measured to calibrate altitude and, consequently, aircraft flight levels. A common and relatively straightforward mean sea-level standard is instead the midpoint between a mean low and mean high tide at a particular location.Sea levels can be affected by many factors and are known to have varied greatly over geological time scales. However 20th century and current millennium sea level rise is caused by global warming, and careful measurement of variations in MSL can offer insights into ongoing climate change.The term above sea level generally refers to above mean sea level (AMSL).

Spherical coordinate system

In mathematics, a spherical coordinate system is a coordinate system for three-dimensional space where the position of a point is specified by three numbers: the radial distance of that point from a fixed origin, its polar angle measured from a fixed zenith direction, and the azimuth angle of its orthogonal projection on a reference plane that passes through the origin and is orthogonal to the zenith, measured from a fixed reference direction on that plane. It can be seen as the three-dimensional version of the polar coordinate system.

The radial distance is also called the radius or radial coordinate. The polar angle may be called colatitude, zenith angle, normal angle, or inclination angle.

The use of symbols and the order of the coordinates differs between sources. In one system frequently encountered in physics (r, θ, φ) gives the radial distance, polar angle, and azimuthal angle, whereas in another system used in many mathematics books (r, θ, φ) gives the radial distance, azimuthal angle, and polar angle. In both systems ρ is often used instead of r. Other conventions are also used, so great care needs to be taken to check which one is being used.

A number of different spherical coordinate systems following other conventions are used outside mathematics. In a geographical coordinate system positions are measured in latitude, longitude and height or altitude. There are a number of different celestial coordinate systems based on different fundamental planes and with different terms for the various coordinates. The spherical coordinate systems used in mathematics normally use radians rather than degrees and measure the azimuthal angle counterclockwise from the x-axis to the y-axis rather than clockwise from north (0°) to east (+90°) like the horizontal coordinate system. The polar angle is often replaced by the elevation angle measured from the reference plane. Elevation angle of zero is at the horizon.

The spherical coordinate system generalizes the two-dimensional polar coordinate system. It can also be extended to higher-dimensional spaces and is then referred to as a hyperspherical coordinate system.

Summit

A summit is a point on a surface that is higher in elevation than all points immediately adjacent to it. The topographic terms acme, apex, peak (mountain peak), and zenith are synonymous.

The term top (mountain top) is generally used only for a mountain peak that is located at some distance from the nearest point of higher elevation. For example, a big massive rock next to the main summit of a mountain is not considered a summit. Summits near a higher peak, with some prominence or isolation, but not reaching a certain cutoff value for the quantities, are often considered subsummits (or subpeaks) of the higher peak, and are considered part of the same mountain. A pyramidal peak is an exaggerated form produced by ice erosion of a mountain top. Summit may also refer to the highest point along a line, trail, or route.

The highest summit in the world is Everest with height of 8844.43 m above sea level (29,029 ft). The first official ascent was made by Tenzing Norgay and Sir Edmund Hillary. They reached the mountain's peak in 1953.Whether a highest point is classified as a summit, a sub peak or a separate mountain is subjective. The UIAA definition of a peak is that it has a prominence of 30 metres (98 ft) or more; it is a mountain summit if it has a prominence of at least 300 metres (980 ft). Otherwise, it's a subpeak.

In many parts of the western United States, the term summit refers to the highest point along a road, highway, or railroad. For example, the highest point along Interstate 80 in California is referred to as Donner Summit and the highest point on Interstate 5 is Siskiyou Mountain Summit.

Topographic map

In modern mapping, a topographic map is a type of map characterized by large-scale detail and quantitative representation of relief, usually using contour lines, but historically using a variety of methods. Traditional definitions require a topographic map to show both natural and man-made features. A topographic survey is typically published as a map series, made up of two or more map sheets that combine to form the whole map. A contour line is a line connecting places of equal elevation.

Natural Resources Canada provides this description of topographic maps:These maps depict in detail ground relief (landforms and terrain), drainage (lakes and rivers), forest cover, administrative areas, populated areas, transportation routes and facilities (including roads and railways), and other man-made features.

Other authors define topographic maps by contrasting them with another type of map; they are distinguished from smaller-scale "chorographic maps" that cover large regions, "planimetric maps" that do not show elevations, and "thematic maps" that focus on specific topics.However, in the vernacular and day to day world, the representation of relief (contours) is popularly held to define the genre, such that even small-scale maps showing relief are commonly (and erroneously, in the technical sense) called "topographic".The study or discipline of topography is a much broader field of study, which takes into account all natural and man-made features of terrain.

Topographic prominence

In topography, prominence measures the height of a mountain or hill's summit relative to the lowest contour line encircling it but containing no higher summit within it. It is a measure of the independence of a summit. A peak's key col (highest gap between two mountains) is a unique point on this contour line and the parent peak is some higher mountain, selected according to various objective criteria.

Topography

Topography is the study of the shape and features of land surfaces. The topography of an area could refer to the surface shapes and features themselves, or a description (especially their depiction in maps).

Topography is a field of geoscience and planetary science and is concerned with local detail in general, including not only relief but also natural and artificial features, and even local history and culture. This meaning is less common in the United States, where topographic maps with elevation contours have made "topography" synonymous with relief.

Topography in 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 techniques, including contour lines, hypsometric tints, and relief shading.

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