The question of which map is the “most accurate” is a fundamental challenge in cartography, the science of mapmaking. Since the Earth is a three-dimensional, curved surface, every flat map is a two-dimensional representation of that sphere. This geometric transformation means no single flat map can perfectly preserve all geographic properties simultaneously. All flat maps are, by mathematical necessity, compromises that prioritize one type of accuracy over others, meaning the choice depends entirely on the map’s intended purpose.
The Mathematical Necessity of Distortion
The problem of creating a world map stems from the impossibility of flattening a sphere without causing stretching, tearing, or compression. Map projection is the mathematical method used to manage and distribute this unavoidable distortion across the map surface.
A sphere possesses constant curvature, while a flat plane has zero curvature. There is no mathematical function that can transform one to the other while maintaining all properties. Cartographers visualize local distortion by projecting tiny, imaginary circles from the globe onto the flat map. These circles transform into ellipses, and their shape and size indicate the type and magnitude of distortion at that specific point.
Distortion is not uniform across a given projection. It generally increases as one moves away from the point or line of tangency or secancy—the places where the flat surface touches or intersects the globe. By selecting different projection methods, mapmakers control where the least and most distortion occurs.
Defining the Types of Accuracy
To manage distortion, map projections are designed to preserve one or more of four core geographic properties: area, shape, distance, and direction. This preservation always comes at the expense of the other properties. A map that preserves the relative size of landmasses is called an equal-area, or equivalent, map.
The relative size of regions is maintained on equal-area maps. Conversely, a map designed to preserve local angles and the true form of small landmasses is called a conformal, or orthomorphic, map. On a conformal map, the shape of a coastline is accurate, though its overall size may be significantly exaggerated or shrunken.
The conflict between these two properties is absolute: a map cannot be both truly equal-area and truly conformal across the entire globe. Preserving distance, known as equidistance, is possible only along specific lines or from one or two central points. Preserving direction, or azimuthal accuracy, means that the compass bearing from a central point to any other point on the map is correct.
Comparing Standard Projections
The Mercator projection, developed in 1569, is historically significant for navigation. Its primary strength lies in its conformality, accurately preserving the shape of small areas. It depicts lines of constant compass bearing, called rhumb lines, as straight segments, making it an invaluable tool for marine navigation.
However, the Mercator projection achieves shape preservation by severely distorting area, a distortion that increases dramatically toward the poles. Landmasses near the equator are represented accurately, but those at high latitudes, such as Greenland, appear vastly larger than their true size.
In contrast, the Gall-Peters projection, a cylindrical equal-area projection, prioritizes the accurate representation of continental area. It ensures that all landmasses are shown in their correct relative proportions, addressing the size biases present in maps like the Mercator. The Gall-Peters map achieves this area accuracy by sacrificing shape, especially near the poles and the equator, resulting in a vertical stretching of landmasses.
The Winkel Tripel projection, introduced in 1921, is widely cited as an effective compromise projection. It aims to minimize three types of distortion: area, direction, and distance. It balances competing properties to produce a visually appealing and balanced representation of the world, featuring curved lines of latitude and longitude. Due to this balanced approach, the National Geographic Society adopted it in 1998 as its standard world map projection.
Selecting the Appropriate Map
The concept of the “most accurate” map is dependent entirely on the intended application, as different tasks require the preservation of different properties. For marine and air navigation, a conformal map like the Mercator projection is preferred because maintaining accurate angles and compass bearings is paramount for plotting a course.
When a map is used for statistical, educational, or political purposes, such as displaying resource distribution or population density, an equal-area projection is necessary. The integrity of relative size must be maintained so that visual comparisons of landmasses do not lead to flawed conclusions.
For general reference, wall maps, or atlases intended to provide a balanced world view, compromise projections like the Winkel Tripel are the best choice. These maps accept minor distortions in all properties to prevent gross errors in any single one. Ultimately, the globe remains the only perfectly accurate model of the Earth’s surface.