Great circle vs Rhumb line

The shortest path on the globe (great circle) and a constant-bearing route (rhumb line) look completely different depending on the projection. Pick a route and a projection to see the contrast.

Map projection:

Straight-line duel

On Mercator, the straight line is the constant-bearing rhumb line.

Map appearance

Choose a background suited to the route and viewing conditions.

Great circle (orthodrome — shortest path)Rhumb line (constant compass bearing)

Map layersProjection diagnostics

Tissot's indicatrices

Equal-sized circles on the globe. Their distortion on the map instantly reveals how the projection alters area and shape.

Area isocolesA

Lines joining places with the same relative area inflation. They work like contour lines on a topographic map of error.

Angular isocolesω

Lines of equal maximum angular deformation. On conformal projections such as Mercator, this layer remains empty.

True-north field↑N

Arrows show where geographic north lies on the screen. Their rotation reveals how a projection alters directions.

Geographic context

Equator, tropics & polar circles

Five major parallels anchor Earth's zones and reveal how the projection stretches high latitudes.

Pick cities:

You can also click any two points on the map to trace your own route.

Example routes:

Distance comparison

Great-circle distance6,854 km

Rhumb-line distance7,349 km

The rhumb line is 495 km (7.2%) longer

Why do the routes differ?

On the Mercator map the rhumb line (a line of constant bearing) is perfectly straight — which made it handy for navigation. But the actual shortest path is the great circle, which on Mercator curves in an arc towards the pole. On the globe and azimuthal projections it's the reverse: the great circle becomes the straight one.

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Live routeWarsaw → New YorkMercator · 6,854 km