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Spherical Earth

The spherical Earth is the scientific consensus that Earth is an oblate spheroid—a sphere slightly flattened at the poles and bulging at the equator—with an equatorial diameter of 12,756 kilometers and a polar diameter of 12,714 kilometers.^[1] This shape arises from gravitational forces during planetary formation, which pull molten material into a compact, roughly spherical form, while the planet's rotation introduces a centrifugal effect that widens the equator by about 42 kilometers.^[2]^[3] The recognition of Earth's sphericity originated in ancient Greece around 500 BCE, when philosophers like Pythagoras proposed a spherical cosmos for aesthetic and mathematical harmony, and Aristotle provided empirical support through observations such as the circular shadow cast on the Moon during lunar eclipses and the hull-first disappearance of ships over the horizon.^[4] By the 3rd century BCE, Eratosthenes of Alexandria calculated the planet's circumference to within a few percent of modern values by comparing the Sun's noon shadow angles between Alexandria and Syene (modern Aswan), assuming parallel solar rays and a known distance of approximately 800 kilometers between the cities.^[4] Centuries of exploration, including maritime circumnavigations by Ferdinand Magellan’s expedition in 1519–1522, further validated the model by demonstrating the planet's continuous curvature without edges.^[5] In the modern era, direct visual confirmation emerged from space missions starting in the late 1950s, with photographs from satellites and crewed flights revealing Earth's rounded silhouette against the cosmos.^[6] Supporting observations include latitude-dependent variations in shadow lengths, the progression of sunsets across time zones due to 24-hour rotation, and horizon effects where distant objects vanish bottom-up, all consistent with a curved surface.^[7] This model underpins fields like geodesy, navigation, and climate science, enabling precise global positioning systems and predictions of gravitational variations that influence sea levels and satellite orbits.^[5]^[3]

Formation and Physical Causes

Planetary Formation Processes

The formation of Earth and its initial spherical shape originated in the protoplanetary disk, a rotating cloud of gas and dust encircling the young Sun approximately 4.6 billion years ago. In the standard core accretion model, microscopic dust grains within this disk collided and adhered due to electrostatic and van der Waals forces, progressively aggregating into larger particles. These grew through further collisions into planetesimals, typically kilometer-scale rocky or icy bodies, which served as the building blocks for protoplanets.^[8] The process was driven by gravitational instabilities and streaming instabilities in the disk, where concentrations of solids exceeded the gas density, facilitating rapid clumping.^[8] As protoplanets like proto-Earth accreted more material, their increasing mass—reaching about $10^{21} kg, roughly the mass of the largest asteroids such as Ceres—enabled self-gravity to dominate over the material's tensile strength. This led to hydrostatic equilibrium, a state where the inward pull of gravity is balanced by outward pressure from the body's interior, naturally yielding a spherical configuration as the lowest-energy shape.^[9] For bodies below this mass threshold, such as most asteroids, gravitational forces are too weak to reshape irregular structures formed by collisions, resulting in potato-like forms held together primarily by material cohesion rather than global equilibrium. Earth's accretion concluded around 4.54 billion years ago, marking the planet's emergence as a fully formed body from the solar nebula. During this early phase, spanning tens of millions of years, intense heat from impacts and radioactive decay triggered core-mantle differentiation: denser iron and nickel sank to form the core, while lighter silicates rose to create the mantle and crust. This internal layering reinforced the spherical symmetry by distributing mass uniformly under hydrostatic balance, establishing the foundational oblate spheroid shape observed today.^[11] Later rotational dynamics introduced minor deviations from perfect sphericity, but the initial form was dominantly spherical due to these formative processes.^[11]

Role of Gravity and Rotation

The shape of Earth is primarily governed by Newton's law of universal gravitation, which states that every particle in the universe attracts every other particle with a force proportional to the product of their masses and inversely proportional to the square of the distance between them, expressed as F = G \frac{m_1 m_2}{r^2}, where G is the gravitational constant. For a non-rotating body in hydrostatic equilibrium, this self-gravitation results in equipotential surfaces that are spherical, as the gravitational potential is symmetric and minimizes the potential energy of the mass distribution.^[12]^[13] Earth's rotation introduces a centrifugal force that counteracts gravity most strongly at the equator, where the rotational velocity is highest at approximately 465 m/s, leading to an outward "bulge" and deformation into an oblate spheroid. With a sidereal rotation period of about 23 hours 56 minutes, this centrifugal acceleration at the equator is roughly 0.034 m/s², reducing effective gravity by about 0.3% compared to the poles and causing the equatorial radius to exceed the polar radius by approximately 21 km.^[14] Models of Earth's figure have evolved from a simple sphere to more precise ellipsoidal representations to account for this oblateness. The World Geodetic System 1984 (WGS84), a standard reference ellipsoid, defines Earth's shape with a semi-major (equatorial) axis of 6,378,137 m and a flattening ratio f \approx 1/298.257, quantifying the compression along the polar axis.^[15] Tidal forces from the Moon and Sun induce minor deformations on Earth's solid body, with amplitudes up to about 30-40 cm in the crust, primarily through differential gravitational gradients that stretch the planet slightly along the Earth-Moon/Sun line. These effects, while measurable, are small compared to the rotational bulge and do not significantly alter Earth's overall sphericity.^[16]

Historical Recognition

Ancient and Pre-Modern Observations

In the 6th century BCE, the Greek philosopher Pythagoras proposed that the Earth was spherical, extending his philosophical belief in the perfection of spheres from the cosmos to the planet itself, based on aesthetic and metaphysical grounds rather than empirical evidence.^[17] By the 4th century BCE, Aristotle provided more observational support for a spherical Earth in his work On the Heavens. He noted that ships sailing away from shore disappear hull-first over the horizon, suggesting a curved surface rather than a flat plane.^[18] Aristotle also observed that the visible stars change with latitude: travelers moving north or south see different constellations rise or set, consistent with a spherical geometry where observers occupy different positions on a globe.^[19] Additionally, he pointed to the circular shadow cast by Earth during lunar eclipses as further indication of sphericity.^[19] These ideas influenced later thinkers, including Eratosthenes in the 3rd century BCE, who drew on reports of varying shadows to infer curvature qualitatively before his quantitative calculations. He learned that on the summer solstice, the Sun shone directly into a well at Syene (modern Aswan), casting no shadow, while in Alexandria, shadows were noticeable at noon, implying the Sun's rays struck the surface at different angles due to Earth's curve.^[17] Similar concepts emerged independently in other ancient cultures. In 5th-century CE India, astronomer Aryabhata described the Earth as a sphere in his Aryabhatiya, treating it as a rotating globe suspended in space within his astronomical models.^[20] In the Islamic world during the 11th century, Al-Biruni conducted experiments to demonstrate curvature, such as measuring the dip of the horizon from a mountain height and observing how distant objects appeared lower than expected on a flat plane, confirming the Earth's rounded form.^[21] During the medieval period in Europe, the notion of a spherical Earth persisted among scholars, with the Catholic Church broadly accepting it despite later myths portraying widespread belief in a flat Earth. Early Church fathers like Augustine referenced the Earth's round shape, aligning with classical Greek sources, and by the 12th century, theologians such as Thomas Aquinas integrated Aristotelian evidence into Christian cosmology without controversy.^[22]^[23] This acceptance was rooted in the transmission of ancient texts through monastic and university traditions, ensuring the qualitative observations of sphericity remained foundational.^[24]

Key Measurements and Calculations

One of the earliest quantitative assessments of Earth's size was conducted by the Greek scholar Eratosthenes in the 3rd century BCE. Observing that the Sun was directly overhead at noon in Syene (modern Aswan) on the summer solstice, while in Alexandria it cast a shadow at an angle of 7.2 degrees—equivalent to 1/50th of a full circle—he measured the distance between the two cities as approximately 5,000 stadia and extrapolated the full circumference to about 250,000 stadia, or roughly 40,000 kilometers, remarkably close to the modern value of 40,075 kilometers.^[25]^[26] In the 1st century BCE, the Stoic philosopher Posidonius revised this estimate using astronomical observations of the star Canopus. Measuring the difference in the star's altitude above the horizon from Rhodes and Alexandria—a separation of about 5,000 stadia—he calculated the Earth's circumference as 240,000 stadia, or approximately 39,000 kilometers, slightly underestimating the equatorial value but confirming the spherical scale.^[27]^[25] The 2nd-century CE astronomer Claudius Ptolemy built on these foundations in his seminal work Almagest, assuming Earth's sphericity as a foundational premise for his geocentric model. He refined positional data for stars and planets by adopting a standardized Earth circumference of 180,000 stadia—drawing from Posidonius but adjusted downward— to integrate terrestrial longitudes with celestial coordinates, enabling more precise mappings within the spherical framework.^[28]^[29] During the Renaissance, Ferdinand Magellan's expedition from 1519 to 1522 provided the first empirical confirmation of Earth's global extent through circumnavigation. Covering approximately 60,000 kilometers westward from Spain back to the Atlantic, the voyage—completed by Juan Sebastián Elcano after Magellan's death—demonstrated the planet's vast spherical girth, aligning with ancient estimates and dispelling underestimations of its size.^[30]^[31] Further precision came in 1617 from Dutch mathematician Willebrord Snellius, who employed triangulation across the Netherlands. By chaining angular measurements along a north-south baseline of about 130 kilometers using theodolites, he determined the Earth's circumference to be roughly 38,653 kilometers, an improvement within 3.5% of the actual value and advancing the method for large-scale geodesic surveys.^[32]^[33] In the 18th century, the French Academy of Sciences sponsored expeditions to resolve debates on Earth's exact shape, revealing its oblateness due to rotation. The 1736–1737 Lapland mission, led by Pierre Louis Moreau de Maupertuis, measured a meridian arc near the Arctic Circle at about 57,438 toises (approximately 111.9 km) for one degree of latitude, while the 1735–1745 Peruvian expedition, under Charles Marie de La Condamine and others, found 56,749 toises (approximately 110.6 km) per degree near the equator; these discrepancies confirmed a flattened spheroid, with the equatorial diameter exceeding the polar by roughly 43 kilometers.^[34]^[35]

Modern Scientific Evidence

Astronomical and Observational Proofs

Horizon effects provide a direct observational confirmation accessible to modern skywatchers. When a ship sails away from an observer over a calm sea, the hull disappears below the horizon first, followed by the sails and finally the mast tips, due to the curvature of Earth's surface blocking the lower parts progressively. This sequence reverses as the ship approaches, with the mast appearing before the hull, a pattern observed universally and inconsistent with a flat plane where the entire ship would shrink uniformly until vanishing. Such visibility changes demonstrate that the horizon acts as a curved boundary, aligning with a spherical Earth model.^[36]^[37] The differing visibility of circumpolar stars and constellations across hemispheres further evidences Earth's roundness through positional astronomy. In the Northern Hemisphere, stars near the north celestial pole, such as those in Ursa Minor, remain perpetually above the horizon and circle without setting, while southern constellations like the Southern Cross never rise above the horizon for northern observers. Conversely, southern hemisphere viewers see the Southern Cross as circumpolar but cannot observe northern constellations like the Big Dipper. This hemispheric exclusivity in stellar visibility arises because a spherical Earth positions observers at varying distances from the celestial poles, altering which stars stay above the horizon; on a flat Earth, all stars would be equally visible to all observers without such latitudinal restrictions.^[38]^[39]^[40] Sunset timing variations along lines of latitude offer additional proof from diurnal observations. For observers at the same latitude but separated east-west by longitude, the moment of sunset differs predictably due to Earth's rotation, with the Sun setting later in coordinated universal time (UTC) for those farther east along the parallel, while occurring at similar local solar times. This temporal gradient, where moving eastward delays the apparent sunset relative to a fixed clock, reflects the spherical geometry and rotational dynamics of Earth, as the curved surface ensures that sunlight reaches eastern points after western ones at equivalent latitudes. On a flat Earth, such consistent longitudinal delays in solar events would not occur uniformly.^[41]^[42] In the 19th century, targeted experiments refuted flat-Earth claims by directly measuring curvature over long distances. The Bedford Level experiment, conducted along a six-mile stretch of the Old Bedford River canal in England, was intended by flat-Earth advocate Samuel Rowbotham to demonstrate a level water surface but instead confirmed convexity when naturalist Alfred Russel Wallace adjusted for atmospheric refraction in 1870, revealing a central dip consistent with the spherical curvature approximation of 8 inches per mile squared—matching predictions. Wallace's observations, using marked poles along the canal, showed the midpoint pole submerged relative to the endpoints, proving the water's surface followed Earth's curve rather than remaining flat. This empirical refutation, repeated with variations, solidified observational evidence against planar models using accessible terrestrial surveying.^[43]^[44]

Space-Based and Technological Confirmations

Space-based observations have provided direct visual confirmation of Earth's spherical shape through high-resolution imagery captured from orbit. The iconic "Earthrise" photograph, taken by astronaut William Anders during the Apollo 8 mission on December 24, 1968, depicted Earth as a partially illuminated blue marble rising above the lunar horizon, offering the first color image of the planet from deep space and clearly illustrating its curved silhouette.^[45] Earlier weather satellites, such as NASA's TIROS-1 launched in 1960, began transmitting images of Earth's cloud cover and surface features from low Earth orbit, revealing the planet's rounded horizon in partial views that built toward full-disk imagery.^[46] Contemporary live video feeds from the International Space Station (ISS), streamed in high definition since 2014 via external cameras like the High Definition Earth Viewing (HDEV) experiment, continuously display Earth's curvature as the station orbits at approximately 400 kilometers altitude, with the horizon visibly arching against the blackness of space.^[47] Technological advancements in satellite geodesy, particularly the Global Positioning System (GPS), have enabled precise measurements of Earth's shape, confirming its oblate spheroid form with centimeter-level accuracy. The GPS constellation, consisting of over 30 satellites orbiting at about 20,200 kilometers, uses microwave signals to determine positions on Earth's surface, incorporating models of the planet's ellipsoidal geometry to achieve horizontal accuracies of 1-3 centimeters and vertical accuracies of 2-5 centimeters globally.^[48] These measurements, refined through space-based geodetic techniques like satellite laser ranging and very long baseline interferometry, validate the equatorial bulge of approximately 21 kilometers, a hallmark of the oblate spheroid resulting from rotational forces, and have been instrumental in updating the World Geodetic System (WGS84) reference ellipsoid.^[49] Gravity mapping missions have further substantiated Earth's sphericity by quantifying deviations from a perfect sphere in the geoid—the equipotential surface approximating mean sea level. NASA's Gravity Recovery and Climate Experiment (GRACE), operational from 2002 to 2017, employed twin satellites in a low-Earth orbit to detect monthly variations in Earth's gravity field with a spatial resolution of about 300 kilometers, revealing mass distributions that align with an oblate spheroid perturbed by topographic and density anomalies.^[50] Complementing this, the European Space Agency's (ESA) Gravity field and steady-state Ocean Circulation Explorer (GOCE), active from 2009 to 2013, used a gradiometer to map the geoid at a resolution of 100 kilometers, achieving an accuracy of 1-2 centimeters and confirming undulations up to 100 meters that reflect the planet's rotational flattening.^[51] The successor mission, GRACE Follow-On (GRACE-FO), launched in 2018 and ongoing as of 2025, continues these observations with enhanced laser interferometry, tracking mass redistributions such as groundwater depletion and ice sheet loss at rates of up to 532 gigatons per year in regions like Greenland.^[52] As of 2025, integrations of quantum gravimetry with satellite data are enhancing real-time monitoring of Earth's shape amid climate-induced changes, including subtle alterations to its oblateness from polar ice melt. NASA's Quantum Gravity Gradiometer Pathfinder (QGGPf), demonstrated in ground tests and slated for orbital deployment, employs cold-atom interferometry to measure gravity gradients with sensitivities 100 times greater than classical instruments, enabling detection of mass shifts from ice melt that could redistribute up to 0.3 millimeters annually in sea level equivalents and marginally affect the equatorial bulge.^[53] These quantum sensors, combined with GRACE-FO data, provide continuous tracking of geoid variations driven by climate factors, such as the observed decrease in geoid height over Greenland due to ice loss since 2002, on the order of millimeters per year.^[54] High-altitude balloon experiments have visually debunked flat Earth claims by demonstrating the horizon's drop-off, consistent with spherical geometry. During the 2012 Red Bull Stratos project, skydiver Felix Baumgartner ascended to 39 kilometers in a helium balloon and jumped, with helmet-mounted cameras capturing the Earth's horizon curving distinctly at altitudes above 30 kilometers, where the drop exceeds 3 degrees over a 360-degree view—far beyond what a flat plane would allow.^[55] Similar amateur and scientific balloon flights, reaching 35-40 kilometers, routinely record this curvature, with the visible horizon distance increasing to over 400 kilometers, aligning precisely with predictions from Earth's 6,371-kilometer radius.^[56]

Geometrical and Representational Models

Approximations of Earth's Shape

The simplest mathematical approximation of Earth's shape is a sphere with a mean radius of 6,371 km, which provides sufficient accuracy for low-precision astronomical calculations where rotational flattening is negligible.^[57] A more precise model treats Earth as an oblate spheroid, flattened at the poles due to its rotation, with the equatorial radius exceeding the polar radius by approximately 21 km.^[58] Early refinements included the Clarke 1866 ellipsoid, defined by a semi-major axis of 6,378,206.4 m and inverse flattening of 294.9786982, and the Hayford 1909 ellipsoid, with a semi-major axis of 6,378,388 m and inverse flattening of 296.959.^[59]^[60] The modern standard is the WGS84 ellipsoid, characterized by a semi-major axis a = 6,378,137 m and flattening f = 1/298.257223563, which serves as the reference for global positioning systems.^[58] Beyond the oblate spheroid, the geoid represents an irregular equipotential surface of Earth's gravity field that best approximates mean sea level, coinciding with it over oceans but undulating by up to \pm 100 m over land due to mass variations.^[61] Higher-order models, such as the triaxial ellipsoid, account for minor equatorial asymmetries, where the semi-axes differ slightly (e.g., the western equatorial radius is about 70 m longer than the eastern), providing a closer fit to observed gravitational data for advanced geodetic applications.^[62] Assuming a spherical shape introduces errors in practical uses like navigation; for instance, great-circle distances calculated on a sphere deviate by up to approximately 0.3% from ellipsoidal computations, potentially accumulating to tens of kilometers over long routes.^[63]

Mapping and Projection Techniques

Mapping the spherical Earth onto a flat surface inevitably introduces distortions in shape, area, distance, or direction, as no projection can preserve all these properties simultaneously. These distortions arise because the curved surface of a sphere cannot be represented on a plane without compromise, a fundamental challenge articulated in cartographic theory since the 16th century. Projection techniques aim to minimize relevant distortions based on the map's purpose, such as navigation, thematic analysis, or global visualization.^[64] The Mercator projection, developed by Flemish cartographer Gerardus Mercator in 1569, is a cylindrical conformal projection that preserves local angles and shapes, making it ideal for navigation where straight lines represent constant compass bearings (rhumb lines). In this projection, meridians appear as equally spaced vertical lines, and parallels as horizontal lines, with scale increasing progressively toward the poles, leading to severe area distortions—such as Greenland appearing larger than Africa—particularly beyond 60° latitude. Despite these limitations, it became the standard for nautical charts due to its utility in plotting courses.^[64]^[64] The azimuthal equidistant projection preserves true distances from a central point, rendering meridians as straight lines radiating from the center and parallels as concentric circles, which makes it suitable for polar maps and distance measurements from a specific location. Developed in various forms since antiquity and formalized by figures like Jean Picard in the 17th century, it maintains azimuthal directions accurately but distorts shapes and areas away from the center, with increasing elongation toward the edges. This projection is prominently featured in the flag of the United Nations, where a polar aspect centered on the North Pole symbolizes global unity while accurately depicting distances from the pole.^[64]^[65]^[65] In 1963, American cartographer Arthur H. Robinson introduced the Robinson projection as a compromise pseudocylindrical map designed for world atlases, balancing distortions in area, shape, and distance without adhering to a single mathematical property like conformality or equal-area preservation. It uses predefined tabular coordinates to create visually pleasing representations, with minimal distortion near the equator and central meridians but greater errors at the poles and edges, where continents like Antarctica appear stretched. Adopted by the National Geographic Society in 1988 for its general-purpose thematic maps, it prioritizes aesthetic appeal and readability over strict accuracy for any one metric.^[66]^[66]^[66] The authalic sphere serves as an equal-area approximation of the Earth's ellipsoidal shape, defined as a sphere with the same surface area as the reference ellipsoid (e.g., a radius of approximately 6,371 km for the WGS84 datum), facilitating projections where global statistics like land distribution or population density require undistorted areas. By transforming coordinates to this sphere using authalic latitude, cartographers can construct equal-area maps, such as the Lambert azimuthal equal-area projection, ensuring that regions on the map correspond to true proportional areas on the globe for applications in resource management and environmental modeling.^[64]^[64] Advancements in geographic information systems (GIS) software have revolutionized mapping by enabling 3D globe rendering, which circumvents traditional 2D projection distortions through interactive virtual environments. Tools like Google Earth, launched in 2001 and based on Keyhole technology, overlay geospatial data onto a digital 3D sphere, allowing users to view the Earth without flattening artifacts by rotating and zooming in a perspective that simulates direct observation. This approach, supported by satellite imagery and terrain models, integrates multiple projections dynamically for analysis while preserving spherical geometry, as seen in applications for urban planning and disaster response.^[64]^[67]^[67]

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The Gravity Recovery and Climate Experiment-Continuity mission will extend a decades-long record of following shifting water masses using gravity measurements.Mission · GRACE-FO 3D Model · GRACE Tellus · NASA Satellites Reveal Major...
[55]
NASA-Industry Team Creates and Demonstrates First Quantum ...
Dec 20, 2018 · “With this new technology, we can measure the changes of Earth's gravity that come from melting ice caps, droughts, and draining underground ...Missing: real- oblateness
[56]
The Benefits of Future Quantum Accelerometers for Satellite ...
Sep 1, 2024 · We investigate the benefits of future quantum accelerometers based on cold atom interferometry (CAI) on current and upcoming satellite gravity mission concepts.
[57]
Red Bull Stratos - Discover the incredible story
Here are the key numbers – and the stories behind them – from Red Bull Stratos, the free-fall from space that held millions enthralled 10 years ago. Read Story
[58]
Curvature of the Horizon in High-Altitude Balloon Footage
High-altitude balloon footage is often abused by flat-Earthers to show us that the Earth is flat when seen from a high altitude.Missing: confirming Red Bull Stratos
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Planet Compare - Solar System Exploration - NASA
Equatorial Radius(km), 2,439.7, 6,051.8, 6,371.00, 3,389.5, 69,911, 58,232, 25,362 ... Mean Orbit Velocity(km/h), 170,503, 126,074, 107,218, 86,677, 47,002 ...
[60]
World Geodetic System 1984 (WGS 84) - NGA - Office of Geomatics
Defining Parameters: WGS 84 identifies four defining parameters. These are the semi-major axis of the WGS 84 ellipsoid, the flattening factor of the Earth, the ...
[61]
Datums, projections, and coordinate systems
Mar 13, 2025 · It is a sphere. That is, its equatorial radius of 4.25" is the same as its polar radius. If you could spin a bowling ball so fast that ...Missing: diameter | Show results with:diameter
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[XLS] Ellipsoids - DGIWG Portal
This register provides the allowable ellipsoids and their parameters. The published parameters of Everest 1830 are: a = 20922931.80 Indian feet, b = 20853374. ...
[63]
A tutorial on datums - VDatum - NOAA
The WGS84 ellipsoid differs very slightly from the GRS 80 ellipsoid. The ... ellipsoid and six topocentric parameters expressing origin, and orientation.
[64]
A triaxial reference ellipsoid for the Earth | Journal of Geodesy
Mar 27, 2023 · We present a new, physically motivated triaxial reference ellipsoid for the Earth. It is an equipotential surface in the gravity field and closely approximates ...
[65]
Calculate distance and bearing between two Latitude/Longitude ...
[In fact, the earth is very slightly ellipsoidal; using a spherical model gives errors typically up to 0.3% – see notes for further details]. Great-circle ...<|control11|><|separator|>
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[PDF] Map projections--a working manual - USGS Publications Warehouse
Nov 12, 1987 · This publication is a major revision of USGS Bulletin 1532, which is titled Map. Projections Used by the U.S. Geological Survey.
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[PDF] Maps and Cartography: Map Projections - University Libraries
showing airline distances from that point. ○ An example of a polar Azimuthal Equidistant map projection can be seen on the United Nations flag.
[68]
[PDF] Map Projections - USGS Publications Warehouse
Presented by Arthur H. Robinson in 1963. Pseudocylindrical or orthophanic. (“right appearing”) projection. Sinusoidal Equal Area. Used frequently in atlases ...
[69]
Next-generation Digital Earth - PMC - NIH
Jun 21, 2012 · Google's Keyhole Markup Language allows the user's 2D and 3D data to be readily superimposed on the virtual globe in a variety of formats, ...