Best map projection for sea navigation
For navigating on a constant compass course, use the Mercator projection. Every rhumb line, a route that crosses all meridians at the same angle, is a straight line on it, so the course can be read straight off the map.
Best choice: Mercator
Conformal, cylindrical
On a Mercator map every rhumb line, a route of constant bearing, is a straight line. That is exactly what Mercator designed his map for in 1569.
- Area: distorted
- Shape: preserved
- Distances: distorted
- Angles and directions: preserved
- Continuity: preserved
Also good
No other projection in our catalogue meets this need as well.
What to avoid
Great for comparing sizes, but a constant course comes out curved.
See the problem on the map →A different goal or map shape? Change the answers in the finder →
The rhumb line: one course all the way
Gerardus Mercator designed his projection in 1569 with seafaring in mind. Join the port of departure and the destination with a straight line, measure its angle to the meridian and sail that course. The Mercator chart became the standard for nautical charts because it turns spherical geometry into work with a ruler and a protractor.
The shortest path is something else
A rhumb line is not the shortest path. On long routes far from the equator the great circle can be clearly shorter, so navigators planned it on a gnomonic chart, split it into shorter segments and sailed a constant course on each one.
The route lab shows both lines and the difference in their lengths for the cities you choose.
What Mercator is not good for
Keeping angles costs area, so the same map fails at other jobs.
- Comparing country sizes: scale grows toward the poles, so Greenland looks nearly as large as Africa.
- Mapping polar regions: the poles lie at infinity, so the map has to be clipped.
- Thematic world maps: northern countries get undue weight.
Frequently asked questions
Because on this map a constant compass course is a straight line and angles are preserved. A navigator joins two points with a ruler and reads the course without any calculation.
No, except along the equator and the meridians. Everywhere else the great circle is shorter, and the gap grows on long routes far from the equator.
Usually not on long routes, because they follow paths close to the great circle, which are shorter. A rhumb line helps where keeping a single course simple matters most.
The best projection for other jobs
- Comparing country sizesEqual Earth
- Thematic and data mapsEqual Earth
- Wall maps and postersWinkel Tripel
- Flight routesGnomonic
- Web maps and appsMercator
- Distances from one placeAzimuthal Equidistant
- The Arctic and AntarcticaAzimuthal Equidistant
- Oceans and currentsSpilhaus Projection
- Teaching geographyEqual Earth