Azimuthal equidistant projection
Map projection preserving correct distances and azimuths from a center point.
The azimuthal equidistant projection is an azimuthal map projection that preserves correct distances and azimuth directions from a chosen center point to all other points on the map. It is mathematically equivalent to the exponential map on a sphere and has been used historically for polar maps, star charts, and modern communication planning.
- type
- Map projection
- first_text_description
- 11th-century work by al-Biruni
- also_known_as
- Postel projection (in France and Russia)
- notable_use
- Flag of the United Nations
Lore & Background
The earliest known text describing the azimuthal equidistant projection is an 11th-century work by al-Biruni, though it may have been used by ancient Egyptians for star maps. The projection appears in many Renaissance maps. Another early example is the world map by ‛Ali b. Many modern star chart planispheres use the polar azimuthal equidistant projection. In the 21st century, the polar azimuthal equidistant projection has been adopted by Flat Earthers as a map of the Flat Earth, partly due to its use in the UN flag and its depiction of Antarctica as a ring around the edge of the Earth.
Reader's Guide
The azimuthal equidistant projection is significant because it uniquely preserves both correct distances and correct azimuth directions from a single center point, making it valuable for navigation and communication. Its mathematical definition allows any point on the globe to serve as the center, with all other points plotted at their true great-circle distance and azimuth. This property has made it useful for polar maps, where meridians appear as straight lines and distances from the pole are accurate. The projection appears on the flag of the United Nations, a widely recognized symbol. In practical applications, it helps operators of directional antennas determine the correct azimuth to point toward a distant transmitter or receiver. When centered on a point whose antipode lies on land, that antipode smears into a large circle, distorting nearby landmasses. Despite these limitations, the projection remains in use for star charts and specialized terrestrial maps.
Did You Know?
- The earliest text describing the azimuthal equidistant projection is an 11th-century work by al-Biruni.
- The projection appears on the flag of the United Nations as a polar azimuthal equidistant projection.
Frequently Asked Questions
Who is Azimuthal equidistant projection?
It is an azimuthal map projection that guarantees true distances and true compass bearings from one chosen center point to every other location on the map. In France and Russia, fans also know it by the alias Postel projection.
What are Azimuthal equidistant projection's powers/role?
Its signature ability is preserving both distance and azimuth direction from the center to any other point, making it mathematically equivalent to the exponential map on a sphere. That dual-fidelity trait makes it a go-to tool for polar maps, star charts, and communication-network planning.
Why is Azimuthal equidistant projection important?
It is the projection chosen for the United Nations flag, giving the organization a globally recognized visual identity. It has also served as a workhorse for polar cartography, celestial charts, and modern telecom planning for centuries.
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