A globe is inherently more accurate than any flat map because it is a three-dimensional model of the Earth. Globes are the only representation that can accurately portray the planet’s spherical shape without altering the geographic relationships of its features. A map is a two-dimensional representation of the Earth’s curved surface. This necessary change in dimension is the fundamental source of all map inaccuracies, forcing cartographers to make systematic trade-offs. The process of converting the curved surface into a flat plane is known as projection.
The Geometric Necessity of Distortion
The Earth is not a perfect sphere but an oblate spheroid, meaning it is slightly flattened at the poles and bulges at the equator. This three-dimensional shape possesses intrinsic geometric properties that cannot be preserved when transferred to a two-dimensional surface. This is because a spherical surface cannot be “unrolled” or flattened without tearing, stretching, or compressing its features. The mathematical impossibility of making this conversion without error is the reason every flat map of the world contains some form of distortion.
A helpful way to visualize this problem is to consider trying to flatten the peel of an orange. To get the peel to lay perfectly flat, you would have to either cut it or significantly stretch and warp the pieces. Map projection is the mathematical technique cartographers use to manage these unavoidable errors. The greater the area being mapped, the more pronounced these distortions become due to the Earth’s curvature.
The Four Properties Maps Cannot Preserve
Because of the geometric necessity of distortion, no map can simultaneously preserve four properties: area, shape, distance, and direction. Cartographers must choose which properties to maintain and which to sacrifice when creating a map projection. A map that preserves the relative size of all landmasses is called an equal-area projection, but this comes at the cost of distorting the true shape of the continents.
Conversely, a map that maintains the correct angles and local shapes is known as a conformal projection, but this accuracy in shape leads to an exaggeration of area, particularly near the poles. Distance is preserved only along specific lines or from a single central point on an equidistant map, but never across the entire surface. Direction, or the angle from one point to another, can be preserved only from a central point on an azimuthal map.
Common Projections and Their Cartographic Trade-offs
Cartographers select a map projection based on the map’s intended purpose, prioritizing certain properties. The Mercator projection, created in 1569, is a classic example of a conformal map that prioritizes direction and shape. This projection was invaluable for nautical navigation because a straight line represents a constant compass bearing, making it easy for sailors to plot a course.
However, the Mercator projection severely distorts area, causing landmasses farther from the equator, like Greenland, to appear enormous, often seeming comparable in size to Africa. In reality, Africa is approximately fourteen times larger than Greenland. The Gall-Peters projection, an equal-area map, corrects this by preserving the true relative sizes of the continents, but it achieves this by stretching the shapes of landmasses vertically near the equator and horizontally near the poles.
The Robinson projection is a compromise projection that attempts to strike a balance between all four types of distortion. The Robinson map does not perfectly preserve any single property, but it minimizes overall distortion to create a visually balanced representation of the world. This approach makes it a common choice for general-purpose world maps in textbooks and atlases.
Why Flat Maps Remain Essential
Despite their inherent geometric inaccuracies, flat maps are necessary tools for practical reasons that globes cannot accommodate. The most obvious advantage is portability, as a flat map can be easily folded, stored, or displayed on a screen. This format also allows for the representation of large-scale detail, such as the street layout of a neighborhood, which would be impractical to show on a globe. Flat maps also simplify measurements for local areas, allowing users to quickly measure distances with a ruler and scale bar. Therefore, every map is a compromise, a functional tool designed for a specific use by managing unavoidable distortions.