Frequently Asked Questions
The most-asked questions about map projections & cartography foundations.
What exactly is a map projection?
A map projection is a mathematical method for translating the curved surface of Earth onto a flat plane. Every projection makes unavoidable trade-offs in shape, area, distance, or direction because a sphere cannot be unrolled without tearing or stretching.
Who are the most important historical figures in map projection development?
Gerardus Mercator (1569) is the best-known name for his eponymous cylindrical projection, but Johann Heinrich Lambert, Edmond Halley, and James Norman Robinson also made foundational contributions. In the modern era, Arno Peters and John P. Snyder advanced equal-area work and systematic comparison of projections.
Why can't any single map show everything 'correctly'?
A 2D surface cannot perfectly represent a 3D sphere without some form of distortion, a result rooted in Gauss's Theorema Egregium. Every projection must sacrifice at least one of shape, area, distance, or direction in order to preserve the others.
What are the three main projection families?
Projections are grouped by their developable surface: cylindrical (a cylinder wrapped around the globe), conical (a cone tangent to the sphere), and azimuthal or planar (a flat plane touching the globe at one point). Each family distorts differently depending on how far a location sits from the projection's center or standard lines.
What's the difference between conformal and equal-area projections?
A conformal projection preserves local angles and shapes, making it ideal for navigation charts, but it inflates areas toward the poles. An equal-area projection preserves the relative size of regions but warps their shapes, which suits thematic or statistical mapping.
Why is the Mercator projection so controversial?
Mercator's projection dramatically enlarges high-latitude landmasses like Greenland while shrinking equatorial ones like Africa, creating a visually misleading sense of relative size. It was engineered for rhumb-line navigation in the 16th century, not for general-purpose world maps, yet it still dominates classroom walls and many online tools.
What is the Robinson projection and why did it become popular?
James Norman Robinson introduced his pseudo-conic projection in 1963 as a visual compromise that looks 'natural' to the eye, balancing area and shape distortion without perfectly preserving any single property. It became a default in many atlases after National Geographic adopted it in 1988.
How should a beginner choose a projection for a specific project?
Start by identifying what you need to preserve—shapes for navigation, areas for population or resource maps, distances for route planning—then match that requirement to a projection class. Snyder's 1987 USGS manual or interactive tools like the MapProjections.org chooser can guide the decision.
What are the mathematical foundations behind projections?
At their core, projections are coordinate transformations that map spherical or ellipsoidal coordinates (latitude, longitude) to planar x-y coordinates using trigonometric or transcendental functions. The chosen reference ellipsoid (WGS-84, GRS-80, etc.) and the specific projection formula together determine the final geometry.
Where should a newcomer start learning cartography and projections?
John P. Snyder's 'Map Projections: A Working Manual' (USGS Special Publication 1395) remains the classic hands-on reference, while J.B. Harley's multi-volume 'History of Cartography' provides broader scholarly context. For a gentler entry point, the MapProjections.org gallery and the Krygier & Brewer textbook on cartographic design are both accessible and well-illustrated.