PLEN

Gnomonic projection

Neither equal-area nor conformalPerspective azimuthalCreator: Unknown; traditionally, though speculatively, attributed to Thales of MiletusYear: 6th century BC

A gnomonic map does one thing uniquely well: it turns every great circle into a straight line. The cost appears immediately: the farther from the center, the faster the world races toward infinity.

Projection guide

The shortest route gets a ruler

Imagine a lamp at Earth's center and a plane touching the globe. Point shadows land on the plane, and the planes of all great circles intersect it in straight lines.

That is why this is not a whole-world atlas but a precise window aimed at a particular problem: a route, ocean, or hemisphere. Change the route and the map center must change too.

Global Cartographic Grid

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Distortion Properties

PropertyCharacteristic
Area
DistortedDistorted: grows rapidly toward the edge of the view; moderate only within about 30° of the center
Shape
DistortedReasonable only near the center; heavily stretched near the edge
Distances
DistortedDistorted; true only at the very center of the map
Angles and directions
DistortedDistorted; accurate only at the center. In return, every great circle is a straight line
Continuity
PartiallyLess than a hemisphere: points 90° from the center lie at infinity, so a map usually covers at most a third of the globe

History & Origin

One of the oldest perspective projections. Points on the sphere are projected from Earth's center onto a tangent plane. Its unique property is that every great-circle arc becomes a straight line.

Applications

Planning shortest long-distance routes, aviation and marine navigation, and teaching the contrast between great circles and rhumb lines. A route planned on a gnomonic chart was traditionally transferred in segments to a Mercator chart.

How to read this map

A lamp at the globe's center casts a shadow onto a tangent sheet.

  • A straight line means a great circle, not a constant bearing.
  • The center is the most reliable part of the map.
  • The edge is a mathematical limit, not the end of the world.

What you gain and lose

It preserves straight great-circle routes at the cost of area, shape, and full-globe coverage.

Best for

Planning shortest routes and explaining great-circle geometry.

Avoid for

Whole-world maps, area comparison, and regions near the view boundary.

Not sure this projection fits your map? Answer three questions in the finder →

Want to see it next to another projection? Compare: Gnomonic vs Mercator →

TEST THIS PROJECTIONOpen the interactive map: Gnomonic projection →GREAT CIRCLE VS RHUMB LINESee routes in Gnomonic projection →
Take the challenge

Can you recognize this projection without the label?

The projection quiz uses graticules and world outlines, so it is a natural next step from this page.

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Daily challenge

One attempt, the same set for everyone

Size illusion · Build a streak and come back tomorrow for another map.

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✦ How do different countries look in this projection?

Analyze shape distortions of 5 countries in this cartographic projection and test them in the sandbox.

Poland
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A useful starting point for European route demonstrations.

Test on map →
United States
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Transatlantic routes reveal the contrast with Mercator.

Test on map →
Greenland
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Greenland looks calm near the center and explodes in scale near the edge.

Test on map →

Facts worth remembering

  • The hemisphere boundary lies at infinity.
  • Navigators transferred points from a straight gnomonic route onto a Mercator chart.
  • It is the only standard projection that straightens every great circle.

Compare with other projections

The best internal links are the ones that help you think. These projections show different answers to the same problem: how to flatten a sphere.

Conformal, cylindricalMercator projectionConformal, cylindrical. Compare how shapes, area, and readability change.Neither equal-area nor conformal, perspective azimuthalOrthographic projectionNeither equal-area nor conformal, perspective azimuthal. Compare how shapes, area, and readability change.Equidistant, azimuthalAzimuthal equidistant projectionEquidistant, azimuthal. Compare how shapes, area, and readability change.

Keep reading about maps that reshape intuition

Gnomonic vs Mercator: which straight line is shortest?Two maps, two straight lines, and two different questions: shortest route versus constant compass bearing.Great circle vs rhumb line: why the shortest route looks longerThe great circle is the shortest path on a globe, the rhumb line a route of constant bearing. We explain why planes fly along a curve and how to check it.Why do airlines fly in arcs? Great circle vs rhumb lineWhy does a flight route look curved on a map? Learn about great circles, rhumb lines and the difference between a shortest spherical path and a real flight.

Frequently Asked Questions

Every great circle lies in a plane through Earth's center. Projecting from that same center makes its intersection with the map plane a straight line.

Points 90° away from the center project to infinity, so a practical map must be clipped before the hemisphere boundary.

No. It is the shortest great-circle route, but its bearing usually changes. A constant-bearing route is straight on Mercator.