An azimuthal map projection is a map projection where the globe is projected onto a flat plane tangent to the globe at a specific point, or onto a plane parallel to the plane containing a great circle.
This type of projection is characterized by the fact that it preserves directions (azimuths) from a central point. Imagine placing a piece of paper flat against one point on a globe and projecting the Earth's surface onto it. The point where the paper touches the globe becomes the center of the projection.
Key Characteristics
- Central Point: Azimuthal projections are always centered on a specific point on the Earth (like a pole or a city).
- True Directions: Directions (azimuths) from this central point are shown correctly on the map.
- Distortion: Distortion increases away from the central point. What is preserved or distorted (areas, shapes, distances) depends on the specific type of azimuthal projection.
Example: The Azimuthal Equidistant Projection
As stated in the provided reference: The azimuthal equidistant projection is an azimuthal map projection.
It has particularly useful properties:
- Correct Distances: All points on the map are at proportionally correct distances from the center point.
- Correct Azimuths: All points on the map are at the correct azimuth (direction) from the center point.
This makes the azimuthal equidistant projection especially useful for applications where understanding directions and distances from a single location is critical, such as plotting airline routes or showing the view from a pole.
How They Work
While the specifics vary, the core idea involves projecting points from the Earth's surface onto a plane. The perspective point for the projection can be at the center of the Earth, at the antipodal point, or even at infinity, leading to different azimuthal variants. The plane is typically tangent at the chosen central point, but it can also be a cutting plane or a parallel plane in some mathematical definitions.
Common Azimuthal Projections
Although there are many variations, here are a few common types:
| Projection Name | Property Preserved from Center Point | Other Properties | Typical Use Cases |
|---|---|---|---|
| Azimuthal Equidistant | Distance and Azimuth | Areas/Shapes distorted | Flight paths, seismic maps, radio communication |
| Azimuthal Equal-Area | Azimuth (from center) | Areas preserved | Distribution maps, representing hemispheres |
| Gnomonic | Azimuth (from center) | Great Circles as Straight Lines | Navigation, seismology |
| Stereographic | Azimuth (from center), Conformality (locally) | Shapes preserved (locally) | Mapping polar regions, geological mapping |
Note: While Azimuthal Equal-Area, Gnomonic, and Stereographic projections preserve azimuths from the center point, they differ in what other properties they preserve.
For a broader look at how different projections represent the Earth, you can explore resources on map projections.
Practical Insights
- Azimuthal projections are often used for mapping polar regions, hemispheres, or showing relationships (like distances and directions) from a specific point of interest.
- The distortion away from the center point means that areas far from the center appear stretched or compressed depending on the specific projection type.
Understanding the central point and the properties preserved from that point is key to interpreting maps made with azimuthal projections.
