How a globe becomes a flat map
Paper cannot be wrapped smoothly around a ball, but it can be rolled into a cylinder or a cone, or laid flat. Classic projections wrap one of these surfaces around the globe, transfer the map onto it, and then unroll it. Three choices describe the result: the class (which surface), the case (whether it touches or cuts the globe) and the aspect (where it sits on the globe).
The magenta circles are all the same size on the globe. Watch how they grow, shrink or stretch on the paper.
Lamps make the idea easy to see, but most named projections, such as Mercator, Albers and the azimuthal equidistant, are calculated with formulas instead. They still belong to a class: the class tells you the shape of the grid and where the map is most accurate.
Common projections by class
Every projection in this app, grouped by the surface it comes from. Select a name to open it.
- Position
- Area scale
- Angular distortion
Drag the map to move its centre. Click the map first to use the arrow keys.
- Area spread
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- Area distortion (RMS)
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- Mean angular distortion
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- Share of globe shown
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Area spread is the ratio between the most inflated and most shrunken areas, ignoring the top and bottom 5%. The histograms weight every point by its area on the globe.
Compare all projections
Every projection is measured with its default settings, the same way the analysis panel measures the current one. Maps toward the bottom left keep both areas and shapes more truthful. Projections that show only part of the globe are drawn as hollow circles and measured over the part they show.
| Projection | Family | Area distortion (RMS log₂) | Mean angular distortion | Globe shown |
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Batch convert
Reproject many equirectangular (2:1) images at once with the current projection, aspect and output settings, then save them together as a ZIP file.