Why Map Projections Distort Landmass Size

Every flat map of the Earth is a compromise. Because the Earth is a sphere (more precisely, an oblate spheroid), any attempt to flatten its surface onto a plane inevitably introduces distortion. Map projections are mathematical transformations that convert the three-dimensional globe into two dimensions. No projection can preserve all four spatial properties—area, shape, distance, and direction—simultaneously. The choice of projection determines which properties are preserved and which are sacrificed. When the goal is to compare the true size of countries and continents, equal-area projections are essential.

The most famous example of area distortion is the Mercator projection, created in 1569 for nautical navigation. It preserves angles (conformal) and local shapes, making it ideal for plotting straight-line compass bearings. However, to achieve this, the projection dramatically exaggerates the size of landmasses at high latitudes. Greenland appears nearly as large as Africa on a Mercator map, even though Africa is about 14 times larger. Similarly, Antarctica stretches across the entire bottom of the map, and Russia looms far larger than it does in reality. This distortion has led to widespread misconceptions about global geography.

How Equal-Area Projections Preserve True Size

Equal-area projections, also known as equivalent projections, ensure that the area of any region on the map is proportional to its actual area on the Earth’s surface. If a country occupies 2% of the Earth’s land area, it will cover exactly 2% of the map’s land area (within the projection’s mathematical limits). This property makes equal-area projections indispensable for thematic mapping—choropleth maps of population density, vegetation zones, or resource distribution, for example—where visual area comparisons must correspond to real-world statistics.

The Gall-Peters Projection

The Gall-Peters projection, developed in the 19th century and revived in the 1970s by Arno Peters, is a cylindrical equal-area projection. It maintains area accuracy at the cost of shape distortion: landmasses near the equator appear vertically stretched, while those near the poles appear horizontally compressed. This projection gained notoriety for its political implications, as it counters the Eurocentric bias of the Mercator map by making developing nations in Africa and South America appear closer to their true proportions. Critics argue that its severe shape distortion makes it less intuitive for general reference. Nevertheless, it remains a standard choice in educational contexts where area comparison is paramount. National Geographic has explored the history and controversy surrounding this projection.

The Mollweide Projection

The Mollweide projection, invented by Carl Mollweide in 1805, is an equal-area pseudocylindrical projection. It presents the globe in an elliptical shape, with the central meridian as a straight line and parallels as curved lines. The distortion of shapes is moderate, with minimal distortion near the central meridian and increasing towards the edges. The Mollweide projection is often used for world maps in atlases and classroom wall maps because it provides a pleasing visual balance between area accuracy and shape recognition. Its major limitation is that the outer parts of the map are heavily compressed, making high-latitude regions appear narrower than they are.

Goode's Homolosine Projection

Goode’s Homolosine projection, developed by John Paul Goode in 1923, is an interrupted equal-area composite projection. To reduce shape distortion, the world is split into several lobes, each with its own central meridian. This creates a map that looks like a series of gores—like peeling an orange and flattening the rind. The trade-off is that the projection breaks the ocean into separate sections, which can hinder global continuity. However, it excels at preserving both area and shape for individual continents, making it a favorite for landmass-centric maps. The projection is commonly used for maps showing global vegetation, climate zones, and other phenomena where area integrity is critical.

The Winkel Tripel Projection

The Winkel Tripel projection, proposed by Oswald Winkel in 1921, is a compromise projection that is not strictly equal-area but approaches area accuracy while also preserving reasonable shape and distance. It is a modification of the Aitoff projection, averaging coordinates from the equirectangular and Mollweide projections. The result is a map that achieves a low overall distortion score—a property often measured by the Goldberg-Gott metric. The Winkel Tripel projection has become the standard for many reference world maps, including those used by the National Geographic Society since 1998. While not perfectly equal-area, its distortion of area is minimal enough that it is often grouped with equal-area projections for general-purpose use. It is particularly effective for showing landmass sizes with less shape deformation than many strict equal-area projections.

Comparing the Top Equal-Area and Compromise Projections

No single projection is best for every scenario. The following table summarizes key characteristics:

  • Gall-Peters: Cylindrical equal-area. Shape distortion is high, especially at mid-latitudes. Best for area comparisons when shape is secondary.
  • Mollweide: Pseudocylindrical equal-area. Moderate shape distortion, symmetrical. Good for global thematic maps.
  • Goode’s Homolosine: Interrupted equal-area. Low shape distortion per continent but disrupted oceans. Ideal for land-focused mapping.
  • Winkel Tripel: Compromise projection (not strictly equal-area). Low overall distortion of area, shape, and distance. Best for general reference wall maps.
  • Eckert IV: Another pseudocylindrical equal-area projection. Similar to Mollweide but with straight parallels. Suitable for world maps with less polar compression.
  • Equirectangular (Plate Carrée): Simple cylindrical, not equal-area. Grossly distorts area at high latitudes. Rarely used for accurate size representation.

For those who need absolute area fidelity, the Hobo–Dyer projection is a lesser-known cylindrical equal-area variant that attempts to reduce shape distortion by moving the standard parallels to 37°N and 37°S. It is sometimes used in educational atlases seeking an alternative to Gall-Peters.

Limitations of Equal-Area Projections

While equal-area projections are the gold standard for showing true landmass size, they come with inherent drawbacks. The most significant is shape distortion. In the Gall-Peters projection, for instance, Africa appears stretched vertically and compressed horizontally, making its familiar outline unrecognizable. This can confuse map readers who are accustomed to the conformal shapes of the Mercator projection.

Furthermore, equal-area projections often distort angles and directions. A ship’s captain cannot plot a straight-line course on a Gall-Peters map and expect to travel in a great-circle route. Navigation applications require conformal projections like Mercator or the Lambert Conformal Conic.

Another limitation is the interruption of continuity. Goode’s Homolosine breaks the ocean into pieces, which can obscure transoceanic relationships and migratory patterns. Many users find interrupted maps disorienting because they must mentally stitch the lobes back together.

Finally, no equal-area projection can perfectly represent the entire globe without some form of extreme distortion at the edges. The user must always consider the scale and the region of interest. For example, the Mollweide projection compresses high-latitude regions along the sides, making Scandinavia appear thinner than it is. Such trade-offs are inevitable.

How to Choose the Right Projection for Showing Landmass Size

Selecting a projection depends on the map’s purpose, audience, and the regions being emphasized. Here are practical guidelines:

  • For classroom education and global thematic maps: Use the Mollweide or Goode’s Homolosine projection. These provide a balanced view of landmass sizes with recognizable continent shapes.
  • For political or social justice-oriented mapping: The Gall-Peters projection is often favored to highlight the true area of developing nations. However, be aware that its extreme shape distortion may reduce readability for general audiences.
  • For professional reference world maps: The Winkel Tripel projection is the industry standard. Its compromise nature offers low overall distortion, making it suitable for atlases, wall maps, and geographic encyclopedias.
  • For detailed continental studies: Use an interrupted projection like Goode’s Homolosine, which minimizes shape distortion within each landmass. Alternatively, a Lambert Azimuthal Equal-Area projection centered on the continent of interest provides excellent accuracy for a single region.
  • For web mapping and online interactive tools: The Web Mercator projection (EPSG:3857) dominates due to its computational simplicity and seamless zoom levels. However, it is not equal-area and should be used cautiously when comparing sizes. Many modern web applications now offer a projection toggle, allowing users to switch to a true equal-area view for area comparisons.

The Science Behind the Distortion: Tissot’s Indicatrix

To understand how a projection distorts the globe, cartographers use Tissot’s indicatrix. This is a set of infinitesimally small circles drawn on the globe. When projected onto a flat map, these circles become ellipses. The size of the ellipse indicates area distortion; the shape (eccentricity) indicates angular distortion. On an equal-area projection, all ellipses have the same area as the original circle, but their shapes vary. On a conformal projection like Mercator, the ellipses remain circular (no angular distortion) but drastically increase in size toward the poles. The Winkel Tripel projection produces ellipses that are relatively small and close to circular across most of the map, demonstrating its low overall distortion. The US Geological Survey (USGS) provides detailed publications on Tissot’s indicatrix and map projection selection for advanced users.

Real-World Impacts of Map Projection Choice

The choice of map projection is not just a technical decision; it shapes public perception and even policy. The Mercator projection’s exaggeration of the Global North has been criticized for reinforcing colonial-era worldviews, making Europe, North America, and Russia appear dominant in area. Conversely, the Gall-Peters projection was embraced by organizations like UNESCO to promote a more equitable view of global land distribution.

In 2017, the Boston Public Schools system adopted the Gall-Peters projection in classrooms, sparking a national conversation about the political dimensions of cartography. Many educators now use a combination of projections, teaching students to critically evaluate the biases inherent in any map. A helpful resource is the Radical Cartography website, which explores how different projections influence our understanding of the world.

Practical Tips for Using Equal-Area Maps

If you are creating or selecting a map that must show true landmass size, keep these points in mind:

  1. Verify the projection: Many free online map images are mislabeled. Always check the metadata or source description. Reliable sources include the Natural Earth data project, which provides shapefiles with known projections.
  2. Use appropriate software: GIS tools like QGIS and ArcGIS allow you to switch between projections on the fly. For quick comparisons, use interactive web tools that overlay the same data under different projections.
  3. Educate your audience: If you present a map using an equal-area projection, add a brief note explaining the choice. For example, “This map uses the Mollweide projection to accurately compare the spatial extent of different countries.” This helps viewers understand why the map looks different from common reference maps.
  4. Consider scale: Equal-area properties hold for the entire map, but local distortion of shape can be severe. For regional maps (e.g., a single continent), choose a projection centered on that region, such as the Lambert Azimuthal Equal-Area projection, which minimizes both area and shape distortion within the focus area.
  5. Combine with insets: When a single equal-area projection cannot serve all purposes, use inset maps with different projections. A main world map in Mollweide can be supplemented with insets in Mercator for navigation or in conformal projections for detailed shape recognition.

Conclusion: No Perfect Map, but Plenty of Good Choices

The question “Which projection is best for showing true landmass size?” has a clear answer: Equal-area projections are the only faithful representations of area. Among them, the Mollweide, Goode’s Homolosine, and Gall-Peters each offer different trade-offs between shape distortion and visual continuity. The Winkel Tripel projection is a powerful compromise that comes close to equal-area while maintaining a more familiar appearance. The key is to match the projection to the task: thematic mapping demands strict area accuracy, while general reference may benefit from a compromise.

Understanding map projections empowers map readers to look critically at the maps they encounter daily—whether in news articles, textbooks, or weather reports. Every map is a point of view, and knowing the projection behind it is the first step toward seeing the world more clearly.