What is a geographic coordinate system (GCS), and how does it function?

A geographic coordinate system (GCS) is a spherical or geodetic coordinate system used to define locations directly on Earth using latitude and longitude. It is the oldest, simplest, and most widely used type of spatial reference system, forming the basis for many others.

How does a geographic coordinate system differ from a Cartesian coordinate system?

While both use coordinate tuples, geographic coordinate systems are not Cartesian because their measurements are angles, not linear distances on a flat plane. They describe positions on a curved surface, unlike Cartesian systems which operate in a flat, two-dimensional or three-dimensional space.

What essential components, beyond latitude and longitude, are needed for a complete GCS specification?

A complete GCS specification, as defined by standards like EPSG and ISO 19111, requires the inclusion of a chosen geodetic datum. This datum specifies the reference ellipsoid and how it is oriented to the Earth, as different datums will result in different latitude and longitude values for the same physical location.

Who is credited with the invention of the geographic coordinate system, and what was their contribution?

The invention of the geographic coordinate system is generally attributed to Eratosthenes of Cyrene, who composed his *Geography* in the 3rd century BC. He established a system for measuring and mapping locations on Earth.

What specific improvements did Hipparchus introduce to the early geographic coordinate system?

About a century after Eratosthenes, Hipparchus improved the system by determining latitude using stellar measurements rather than solar altitude. He also determined longitude by timing lunar eclipses, a more accurate method than the previous reliance on dead reckoning.

How did Marinus of Tyre and Ptolemy contribute to the development of latitude and longitude measurements?

Marinus of Tyre compiled an extensive gazetteer and created a mathematically plotted world map using coordinates measured east from a prime meridian. Ptolemy later adopted and refined this system in his *Geography*, measuring latitude from the Equator, which became influential for centuries.

How is latitude defined in relation to the Earth's equator and surface point?

Latitude is defined as the angle formed by the plane of the equator and a line connecting a point on the Earth's surface to a second point on the equatorial plane. This second point varies depending on the specific coordinate system used (astronomical, geodetic, or geocentric).

What are the three distinct ways latitude is defined based on different coordinate system types?

Latitude can be defined based on: 1) the extension of the plumb bob vertical from the surface point intersecting the equatorial plane (astronomical), 2) the normal vector from the ellipsoid surface intersecting the equatorial plane (geodetic), or 3) the center of the Earth itself (geocentric).

What are parallels, and how do they relate to the equator?

Parallels are circles on the Earth's surface formed by joining all points of the same latitude. They are parallel to the equator and to each other, running east-west.

How is longitude defined, and what is the significance of the prime meridian?

Longitude is defined as the angle, measured east or west, between a reference meridian (the prime meridian) and another meridian that passes through a specific point on Earth's surface. The prime meridian serves as the zero-degree reference for longitude measurements.

What is the international prime meridian, and where is it located?

The international prime meridian is the meridian that passes through the British Royal Observatory in Greenwich, England. It serves as the 0° longitude line for the global geographic coordinate system.

What is a graticule, and where is its origin point often humorously referred to as Null Island?

A graticule is the visual grid formed on a map by lines of latitude and longitude. The origin point (0° latitude, 0° longitude) of this system is located in the Gulf of Guinea, approximately 625 km south of Tema, Ghana, a location facetiously called Null Island.

What is the purpose of a geodetic datum in a geographic coordinate system?

A geodetic datum is essential for precisely measuring actual locations on the physical Earth using theoretical coordinates like latitude and longitude. It binds a mathematical model of the Earth's shape (like a reference ellipsoid or geoid) to the actual Earth.

What is the difference between a horizontal datum and a vertical datum?

A horizontal datum is used to precisely measure latitude and longitude, typically referencing a reference ellipsoid. A vertical datum, on the other hand, is used to measure elevation or altitude, usually referencing a geoid model.

How do different geodetic datums lead to different coordinate values for the same location?

Different datums use different reference ellipsoids or orientations to the Earth, effectively shifting the coordinate system. This means the same physical point on Earth will have different latitude and longitude values depending on which datum is used for measurement.

Why is it crucial to specify the datum when using spatial reference systems or map projections?

Since all spatial reference systems and map projections are ultimately calculated from latitude and longitude, specifying the datum is crucial for accuracy. Without it, users might interpret coordinates incorrectly, leading to significant positional errors, as different datums can result in shifts of hundreds of meters.

What are examples of global datums, and what phenomena do they account for?

Examples of global datums include the various realizations of WGS 84, used for the Global Positioning System (GPS), and the International Terrestrial Reference System and Frame (ITRF). These global datums account for phenomena like continental drift and crustal deformation.

What are some examples of regional datums, and what is their typical characteristic?

Regional datums are often defined by national cartographical organizations and fit an ellipsoid best to a specific portion of the Earth. Examples include the North American Datums, European Datum 1950 (ED50), and Ordnance Survey Great Britain 1936 (OSGB36).

How does the WGS 84 datum differ from the OSGB36 datum in Greenwich?

In Greenwich, the WGS 84 datum differs from the OSGB36 datum by approximately 112 meters. Other datums like ED50 can differ even more, ranging from about 120 to 180 meters.

What natural Earth movements can affect the accuracy of geographic coordinates over time?

Natural Earth movements such as continental plate motion, subsidence due to weather systems, and diurnal Earth tidal movements can cause physical points on the surface to shift. Additionally, post-glacial rebound, like the rising of Scandinavia, also alters positions relative to datums.

What is the approximate length of one degree of latitude at the Equator on the WGS 84 spheroid?

On the WGS 84 spheroid at sea level at the Equator, one degree of latitude measures approximately 110.6 kilometers. This is derived from the length of a latitudinal minute (1843 m) and second (30.715 m).

How does the length of one degree of longitude vary with latitude?

The length of one degree of longitude decreases as latitude increases because the lines of longitude (meridians) converge at the poles. For instance, at the Equator, a longitudinal degree is about 111.3 km, while at 60° latitude, it is approximately 55.8 km.

What is the formula provided for calculating the length of a degree of latitude on the WGS 84 spheroid?

The length in meters of a degree of latitude at latitude φ on the WGS 84 spheroid is given by the formula: 111132.92 - 559.82 cos(2φ) + 1.175 cos(4φ) - 0.0023 cos(6φ).

What is the formula provided for calculating the length of a degree of longitude on the WGS 84 spheroid?

The length in meters of a degree of longitude at latitude φ on the WGS 84 spheroid is calculated using the formula: 111412.84 cos(φ) - 93.5 cos(3φ) + 0.118 cos(5φ).

How can the length of a longitudinal degree be approximated using a spherical Earth model?

Assuming a spherical Earth, the length of a longitudinal degree at latitude φ can be approximated by the formula (π/180) * Mr * cos(φ), where Mr is Earth's average meridional radius (approximately 6,367,449 meters). This provides a simpler, though less precise, estimate.

What are the approximate lengths of a longitudinal degree, minute, and second at the Equator, based on the table?

Based on the table provided, at the Equator (0° latitude), one longitudinal degree measures approximately 111.3 km, one minute is about 1.855 km, and one second is approximately 30.92 meters.

According to the table, what is the length of a longitudinal degree at 60° latitude?

According to the table, at 60° latitude (e.g., near Saint Petersburg), the length of one degree of longitude is approximately 55.80 km.

What is the purpose of alternative encoding schemes for geographic coordinates?

Alternative encoding schemes for geographic coordinates were developed because latitude-longitude pairs can be difficult to communicate and remember. These schemes convert coordinates into alphanumeric strings or words for easier handling.

Name at least three alternative encoding schemes for geographic coordinates mentioned in the text.

Three alternative encoding schemes mentioned are the Maidenhead Locator System (popular with radio operators), Open Location Code (Plus Codes) developed by Google, and Geohash, which is based on the Morton Z-order curve. Other examples include GEOREF, Mapcode, and What3words.

What is the purpose of the 'See also' section in the article?

The 'See also' section provides a list of related concepts and topics that may be of interest to the reader, offering further avenues for exploration beyond the primary subject of geographic coordinate systems. Examples include related systems like GIS, standards like ISO 6709, and other coordinate systems.

What was the primary error in the calculations of Marinus and Ptolemy concerning the Mediterranean Sea?

The primary error made by Marinus and Ptolemy regarding the Mediterranean Sea was underestimating its actual circumference. This led to their degree measurements overstating the length of the Earth west from their reference points.

What is the default datum used by most Global Positioning System (GPS) equipment?

The World Geodetic System 1984 (WGS 84) is the default datum used in most Global Positioning System (GPS) equipment. It is a global datum that provides a consistent reference frame for satellite navigation.

What topic is suggested for further reading related to geographical coordinates?

The 'Further reading' section suggests exploring 'Mathematical data for bibliographic descriptions of cartographic materials and spatial data,' specifically focusing on geographical coordinates, as detailed in a publication by Jan Smits for the ICA.

Where can media related to the geographic coordinate system be found?

Media related to the geographic coordinate system, such as images and other multimedia files, can be found on Wikimedia Commons.

What are the primary parallels of latitude shown in the 'Circles of latitude / meridians' navbox image?

The primary parallels of latitude highlighted in the navbox image include the Equator (0°), the Tropics of Cancer and Capricorn, the Arctic and Antarctic Circles, and lines every 10° north and south up to 80°, with specific emphasis on 45° N/S.

What are the primary meridians of longitude shown in the 'Circles of latitude / meridians' navbox image?

The primary meridians of longitude shown in the navbox image include the Prime Meridian (0°), the 180° meridian, and lines every 10° east and west up to 170°, with specific emphasis on 90° E/W.

What types of authority control databases are referenced in the article?

The article references national authority control databases from Germany (GND), the United States (Library of Congress), France (BnF data), the Czech Republic (NKC), and Israel, as well as other databases like Yale LUX. These databases help standardize information about geographic coordinate systems.

Geographic Coordinate System Wiki: Navigating Our World: The Geographic Coordinate System

Dive in with Flashcard Learning!

When you are ready...
🎮 Play the Wiki2Web Clarity Challenge Game🎮

Understanding the Geographic Coordinate System

Defining Location

A Geographic Coordinate System (GCS) is a spherical or geodetic coordinate system used to measure and communicate positions directly on Earth's surface. It utilizes latitude and longitude, forming the simplest, oldest, and most widely adopted type of spatial reference system.

While it uses coordinate tuples similar to Cartesian systems, GCS is fundamentally angular and operates on a curved surface, not a plane.

Angular Measurements

Latitude and longitude are angular measurements. Latitude measures the angle north or south of the Equator, while longitude measures the angle east or west of a prime meridian. These angles define a point's position on the Earth's spheroid.

A complete GCS specification also includes a chosen geodetic datum, which anchors the mathematical model of the Earth's shape to the physical planet, ensuring consistent measurements.

Foundation for Systems

The GCS serves as the foundational layer for numerous other spatial reference systems and map projections. Understanding its principles is crucial for accurate geospatial analysis, navigation, and cartography.

Its widespread adoption, standardized by bodies like EPSG and ISO 19111, ensures interoperability across diverse applications and technologies.

Historical Evolution

Ancient Origins

The conceptualization of a geographic coordinate system is attributed to Eratosthenes of Cyrene in the 3rd century BC. Later, Hipparchus of Nicaea refined the system by using stellar measurements for latitude and lunar eclipses for longitude.

Marinus of Tyre, in the 1st or 2nd century AD, compiled a significant gazetteer and plotted a world map using coordinates, establishing a prime meridian relative to the westernmost known lands.

Medieval and Renaissance Developments

Ptolemy's influential work in the 2nd century AD adopted the Equator as the zero parallel for latitude. Arabic scholars like Al-Khwarizmi translated and improved upon these works in the 9th century. Mathematical cartography saw a resurgence in Europe around the 15th century with the recovery and translation of Ptolemy's texts.

Standardization

A pivotal moment occurred in 1884 with the International Meridian Conference, where representatives from twenty-five nations agreed to adopt the longitude of the Royal Observatory in Greenwich, England, as the prime meridian. This established a global standard for longitude measurement.

Modern systems like WGS 84 are continuously refined to account for continental drift and Earth's dynamic movements, ensuring ongoing accuracy.

Latitude and Longitude

Latitude ( $φ$ )

Latitude is the angle measured north or south from the Earth's Equator. It defines parallels, circles parallel to the Equator. The North Pole is 90° N, and the South Pole is 90° S. The Equator itself is defined as 0° latitude.

Different coordinate systems define latitude based on astronomical observations, the normal vector to an ellipsoid, or a geocentric perspective.

Longitude ( $λ$ )

Longitude is the angle measured east or west from a reference meridian, typically the Prime Meridian passing through Greenwich, England. Meridians are halves of great ellipses that converge at the poles.

The 180° meridian (180° W and 180° E) is antipodal to the Prime Meridian, though the International Date Line deviates from this line for practical reasons.

The Graticule

The visual grid formed by lines of latitude and longitude on maps and globes is called a graticule. This system allows for the precise specification of any location on the Earth's surface, excluding altitude.

The origin point for this system, where 0° latitude and 0° longitude intersect, is located in the Gulf of Guinea, often facetiously referred to as "Null Island".

The Role of Geodetic Datums

Binding Math to Reality

A geodetic datum is essential for accurately measuring geographic coordinates. It binds a mathematical model of the Earth's shape (like a reference ellipsoid) to the physical Earth.

A horizontal datum defines latitude and longitude, while a vertical datum defines elevation. Using the same datum ensures consistent coordinate values for a given physical point.

Global vs. Regional

Datums can be global, representing the entire Earth (e.g., WGS 84, ITRF), or regional, fitting an ellipsoid to a specific portion of the Earth (e.g., North American Datum, OSGB36).

Different datums can yield different coordinates for the same location due to shifts in their reference frames, necessitating datum transformations for accurate conversions.

Dynamic Earth

Modern global datums, like ITRF, account for dynamic Earth processes such as continental drift, subsidence, and tidal movements. These factors can cause significant positional shifts over time, especially when using older or regional datums.

The accuracy of a GCS is intrinsically linked to the precision and relevance of its underlying datum.

Measuring Distance: Degree Lengths

Latitude Degree Length

The length of a degree of latitude is relatively constant because parallels of latitude are nearly parallel to the Equator. On the WGS 84 spheroid at sea level, one degree of latitude is approximately 110.6 kilometers (or 68.7 miles).

The precise calculation involves complex formulas accounting for the Earth's oblateness:

111132.92-559.82\,cos 2\phi +1.175\,\cos 4\phi -0.0023\,\cos 6\phi

meters per degree latitude.

Longitude Degree Length

The length of a degree of longitude decreases as latitude increases, converging to zero at the poles. On the Equator, it is approximately 111.3 kilometers (69.2 miles).

The calculation for longitude degree length is:

111412.84\,\cos \phi -93.5\,\cos 3\phi +0.118\,\cos 5\phi

meters per degree longitude.

A simplified approximation using a spherical Earth yields ${\frac {\pi }{180}}M_{r}\cos \phi \!$ meters, where $\textstyle M_{r}\,!$ is the Earth's average meridional radius (approx. 6,367,449 m).

Longitudinal Length Equivalents at Selected Latitudes
Latitude	City	Degree	Minute	Second	0.0001°
60°	Saint Petersburg	55.80 km	0.930 km	15.50 m	5.58 m
51° 28′ 38″ N	Greenwich	69.47 km	1.158 km	19.30 m	6.95 m
45°	Bordeaux	78.85 km	1.31 km	21.90 m	7.89 m
30°	New Orleans	96.49 km	1.61 km	26.80 m	9.65 m
0°	Quito	111.3 km	1.855 km	30.92 m	11.13 m

Alternative Encodings

Enhancing Communication

Latitude and longitude pairs can be cumbersome to communicate. Various alternative schemes have been developed to encode these geographic coordinates into more manageable alphanumeric strings or word sequences.

These methods do not represent distinct coordinate systems but offer different ways to express the same positional data.

Common Systems

Notable encoding systems include:

Maidenhead Locator System (for radio operators)
World Geographic Reference System (GEOREF) and Global Area Reference System (GARS)
Open Location Code (Plus Codes)
Geohash
Mapcode
What3words (proprietary word-based system)

Related Concepts

Geodesy and GIS

The study of Earth's shape, orientation, and gravitational field is known as Geodesy. The Geographic Coordinate System is a fundamental tool within Geodesy and Geographic Information Systems (GIS).

GIS integrates hardware, software, and data to capture, manage, analyze, and display all types of geographically referenced information.

Standards and Systems

Key standards and related systems include:

ISO 6709: Standard representation of geographic point location by coordinates.
Decimal Degrees: A common format for expressing latitude and longitude.
Universal Transverse Mercator (UTM): A projected coordinate system that divides the Earth into zones.
Planetary Coordinate Systems: Similar systems adapted for other celestial bodies.

Teacher's Corner

Edit and Print this course in the Wiki2Web Teacher Studio

Edit and Print Materials from this study in the wiki2web studio

Click here to open the "Geographic Coordinate System" Wiki2Web Studio curriculum kit

Use the free Wiki2web Studio to generate printable flashcards, worksheets, exams, and export your materials as a web page or an interactive game.

True or False?

Test Your Knowledge!

Gamer's Corner

Are you ready for the Wiki2Web Clarity Challenge?

Learn about geographic_coordinate_system while playing the wiki2web Clarity Challenge game.

Unlock the mystery image and prove your knowledge by earning trophies. This simple game is addictively fun and is a great way to learn!

Play now

Explore More Topics

Discover other topics to study!

mitt romney 2008 presidential campaign

philippe douste-blazy

References

WGS 84 is the default datum used in most GPS equipment, but other datums and map projections can be selected.

A full list of references for this article are available at the Geographic coordinate system Wikipedia page

Feedback & Support

To report an issue with this page, or to find out ways to support the mission, please click here.

Disclaimer

Important Notice

This page was generated by an Artificial Intelligence and is intended for informational and educational purposes only. The content is based on a snapshot of publicly available data from Wikipedia and may not be entirely accurate, complete, or up-to-date.

This is not professional advice. The information provided on this website is not a substitute for professional consultation in fields such as cartography, geodesy, or geographic information systems. Always refer to official documentation and consult with qualified professionals for specific needs.

The creators of this page are not responsible for any errors or omissions, or for any actions taken based on the information provided herein.

Navigating Our World

💡 Dive in with Flashcard Learning! 💡

Understanding the Geographic Coordinate System 📍

🌍 Defining Location

📐 Angular Measurements

🗺️ Foundation for Systems

Historical Evolution ⏳

🏛️ Ancient Origins

🌍 Medieval and Renaissance Developments

🤝 Standardization

Latitude and Longitude 📐

📏 Latitude (φ)

📏 Longitude (λ)

🕸️ The Graticule

The Role of Geodetic Datums ⚓

🔗 Binding Math to Reality

🌐 Global vs. Regional

⏳ Dynamic Earth

Measuring Distance: Degree Lengths 📏

➡️ Latitude Degree Length

➡️ Longitude Degree Length

Alternative Encodings 🔢

🔤 Enhancing Communication

🔠 Common Systems

Related Concepts 🔗

📊 Geodesy and GIS

📜 Standards and Systems

Teacher's Corner 🧑‍🏫

Edit and Print this course in the Wiki2Web Teacher Studio

True or False? 🤔

❓ Test Your Knowledge! ❓

Gamer's Corner 🎮

Are you ready for the Wiki2Web Clarity Challenge?

Explore More Topics

📜 Discover other topics to study!

References

📜 References

Feedback & Support 👍

To report an issue with this page, or to find out ways to support the mission, please click here.

Disclaimer ⚠️

📜 Important Notice

Dive in with Flashcard Learning!

Understanding the Geographic Coordinate System

Defining Location

Angular Measurements

Foundation for Systems

Historical Evolution

Ancient Origins

Medieval and Renaissance Developments

Standardization

Latitude and Longitude

Latitude ( $φ$ )

Longitude ( $λ$ )

The Graticule

The Role of Geodetic Datums

Binding Math to Reality

Global vs. Regional

Dynamic Earth

Measuring Distance: Degree Lengths

Latitude Degree Length

Longitude Degree Length

Alternative Encodings

Enhancing Communication

Common Systems

Related Concepts

Geodesy and GIS

Standards and Systems

Teacher's Corner

True or False?

Test Your Knowledge!

Gamer's Corner

Discover other topics to study!

References

Feedback & Support

Disclaimer

Important Notice