Maps are fundamental tools in geography, allowing us to understand spatial relationships, navigate the world, and analyze geographic data. However, representing the Earth's three-dimensional surface on a flat, two-dimensional map presents significant challenges. This process, known as map projection, inevitably introduces distortions in shape, area, distance, or direction. Because no single projection can perfectly preserve all of these properties, geographers and cartographers select map projections based on their intended purpose. Understanding the different types of distortions and how they affect different projections is essential for accurately interpreting maps.
Understanding Map Projections
A map projection is a systematic transformation of latitude and longitude coordinates from a spherical Earth onto a flat surface. Since the Earth is an oblate spheroid (slightly flattened at the poles and bulging at the equator), projecting it onto a plane always involves some trade-offs in spatial accuracy.
Why Are Map Projections Necessary?
The Earth's surface is curved, but maps are flat. Without projections, we would not be able to represent large areas on paper or digital screens.
Projections allow for standardized spatial analysis across different regions.
Different projections are useful for specific applications such as navigation, education, or thematic mapping.
Developing Map Projections
To create a projection, cartographers must establish a system for translating the Earth’s curved coordinates into a two-dimensional plane. This involves:
Selecting a projection surface:
Cylindrical (e.g., Mercator)
Conic (e.g., Albers Equal-Area)
Azimuthal (Planar) (e.g., Polar Projection)
Determining distortion trade-offs:
Prioritizing shape, area, distance, or direction.
Accepting that at least one of these properties will be distorted.
Mathematically transforming coordinates:
Formulas are used to convert latitude (φ) and longitude (λ) into x, y coordinates.
Since no map projection can be perfect, all maps contain some misrepresentation of reality.
The Selective Nature of Maps
Maps are not exact representations of reality but interpretations based on selective information. Every map involves:
Generalization: Simplifying or omitting small details to make the map more readable.
Symbolization: Using colors, lines, and symbols to represent different geographic elements.
Projection distortions: Every projection introduces inaccuracies in at least one spatial property.
Thus, while maps are incredibly useful, they must always be critically analyzed to understand their limitations.
Types of Map Distortions
Map projections distort four key spatial properties:
1. Shape Distortion
Occurs when a map does not maintain the correct angles and proportions of landmasses.
A map that preserves shape is called a conformal projection.
Example: Mercator Projection
Maintains true shape of landmasses.
Distorts area, especially near the poles.
2. Area Distortion
Occurs when the relative size of different regions is altered.
A map that preserves area is called an equal-area projection.
Example: Gall-Peters Projection
Shows landmasses in their correct relative size.
Distorts shape, making continents appear elongated or squished.
3. Distance Distortion
Occurs when the scale of distance is not uniform across the map.
A map that preserves distance from a certain point is called an equidistant projection.
Example: Azimuthal Equidistant Projection
Accurately represents distances from the center point of the map.
Distorts shape and area, especially towards the edges.
4. Direction Distortion
Occurs when angles between locations are not maintained correctly.
A map that preserves direction is called an azimuthal projection.
Example: Mercator Projection
Maintains true compass directions.
Distorts area, making high-latitude regions appear much larger than they are.
Common Map Projections and Their Distortions
Mercator Projection (Cylindrical)
Developed by Gerardus Mercator in 1569, this is one of the most famous projections.
Purpose: Navigation.
Strengths:
Preserves shape and direction.
Straight meridians and parallels make compass-based navigation easy.
Weaknesses:
Extreme area distortion: Greenland and Antarctica appear much larger than they are in reality.
Equatorial regions are underrepresented in size.
Mathematically, the Mercator projection formula for a given latitude (φ) and longitude (λ) is:
x = R (λ - λ₀)
y = R ln[tan(π/4 + φ/2)]
where R is the Earth’s radius and λ₀ is the reference longitude.
Peters Projection (Equal-Area)
Developed as a response to Mercator’s distortion.
Purpose: Representing true landmass sizes.
Strengths:
Equal-area projection, meaning all regions are proportionally accurate.
Emphasizes the true size of Africa, South America, and Asia.
Weaknesses:
Distorts shape, making landmasses appear stretched.
Robinson Projection (Compromise)
Developed by Arthur H. Robinson in 1963.
Purpose: General-purpose world maps.
Strengths:
Balances distortions of shape, area, distance, and direction.
More visually appealing for classroom and world atlases.
Weaknesses:
Does not perfectly preserve any single property.
Slight shape distortions near the poles.
Azimuthal Equidistant Projection
Purpose: Displays accurate distances from a central point.
Strengths:
Preserves true distances from the map’s center.
Used for airline routes and radar maps.
Weaknesses:
Distorts shape and area, especially at the edges.
Goode’s Homolosine Projection
Purpose: Represents continents accurately.
Strengths:
Reduces distortions in landmasses.
Useful for geographic comparisons.
Weaknesses:
Interrupted projection, creating gaps in the oceans.
Not suitable for navigation.
Choosing the Right Projection
Different map projections are useful for different applications:
Navigation maps: Mercator Projection (preserves direction).
Global equality representations: Peters Projection (preserves area).
General reference maps: Robinson Projection (compromise between distortions).
Distance-focused maps: Azimuthal Equidistant Projection.
Comparing landmass sizes: Goode’s Homolosine Projection.
Geographers, policymakers, and map users must carefully select projections based on their intended use. A well-chosen projection can enhance understanding, while a poorly chosen one can mislead and distort perceptions of the world.
FAQ
Different map projections exist because no single projection can accurately represent all aspects of Earth’s surface. Every projection introduces distortions in shape, area, distance, or direction, so cartographers select projections based on their intended use. For example, navigational maps use the Mercator projection because it preserves direction, allowing sailors and pilots to chart accurate courses. World political maps often use the Robinson projection, which minimizes distortions for a more balanced appearance. When focusing on landmass size equality, cartographers may use the Peters projection, which maintains correct area proportions. Specialized projections, such as Azimuthal Equidistant, are used when accurate distances from a central point (such as a city) are needed. The choice of projection depends on the geographic purpose, the importance of preserving certain spatial properties, and how the map will be interpreted by the audience. Understanding projections prevents misinterpretation of spatial data and allows for more effective geographic analysis.
Cylindrical, conic, and azimuthal projections each use different geometric surfaces to project the Earth's spherical shape onto a flat plane, leading to unique distortions. Cylindrical projections, such as the Mercator projection, project the Earth onto a cylinder. They preserve direction and distort size, especially near the poles, making Greenland and Antarctica appear much larger than they are. These projections are useful for navigation but misrepresent landmass proportions. Conic projections, like the Albers Equal-Area projection, project the Earth onto a cone and are often used for mid-latitude regions, such as the United States, because they minimize distortion in local areas. However, they become distorted further from the standard parallels. Azimuthal projections, such as the Polar Projection, project the Earth onto a flat plane from a central point. They preserve true distances from the center but distort shape and area, especially near the edges. These are useful for airline routes and radio signals. Each type is selected based on the region and purpose of the map.
Tissot’s Indicatrices are mathematical tools used to visualize distortions in map projections. They consist of small circles placed at different points on a map, which indicate how shape, area, and distance are distorted due to projection. On a perfect map with no distortion, the circles remain uniform and round. However, in distorted areas, the circles become stretched, compressed, or skewed. For example, in the Mercator projection, Tissot’s Indicatrices appear larger at the poles, showing the severe area distortion. In the Peters projection, they appear vertically stretched, indicating shape distortion. In the Robinson projection, the circles gradually distort towards the map’s edges, highlighting the compromise approach used to balance distortions. Geographers and cartographers analyze Tissot’s Indicatrices to determine how a projection affects different parts of the world and to choose the best projection for a given purpose. This tool is essential in understanding and correcting misinterpretations of spatial relationships on maps.
Map projections can shape perceptions of the world by exaggerating or diminishing the prominence of certain regions. The Mercator projection, widely used in classrooms and online maps, inflates the size of Europe and North America while shrinking Africa and South America. This has contributed to Eurocentric biases, making developing nations appear smaller and potentially less significant. In contrast, the Peters projection corrects this by presenting all landmasses in their true relative size, promoting a more equal representation of global geography. Additionally, distorted projections can affect geopolitical views, influencing how nations perceive their own importance, power, and influence. For example, the Soviet Union historically favored projections that emphasized its vast land area, reinforcing its global presence during the Cold War. Similarly, national and regional maps often use projections that center their own country, subtly affecting cultural and political identity. Understanding projection distortions is crucial in avoiding biased worldviews and promoting geographically accurate education.
No single map projection is universally the best because every projection involves trade-offs in spatial accuracy. Each projection is designed for a specific purpose, meaning that what is "best" depends on the intended use of the map. For example, the Mercator projection is ideal for navigation due to its ability to preserve direction, but it is not suitable for accurately representing land area. The Peters projection is great for representing landmass proportions, but it distorts shape, making continents appear stretched. The Robinson projection is a compromise, balancing distortions in shape, area, distance, and direction, making it suitable for general reference maps, but it does not perfectly preserve any one property. Even the most advanced computer-generated maps must deal with projection distortions. Instead of seeking a "perfect" projection, geographers choose the most appropriate one based on the specific needs of the map’s audience and application.
Practice Questions
Explain how map projections introduce distortions, and describe how the Mercator and Peters projections differ in terms of distortion.
Map projections distort the Earth's surface because they transfer a three-dimensional sphere onto a two-dimensional plane. This process causes inaccuracies in shape, area, distance, or direction. The Mercator projection preserves shape and direction, making it useful for navigation. However, it distorts area, enlarging high-latitude regions like Greenland and Antarctica. In contrast, the Peters projection preserves area but distorts shape, making continents appear stretched or squished. The Peters projection corrects size disparities seen in Mercator maps, particularly highlighting the true size of Africa and South America. Each projection serves different purposes, demonstrating the challenges of accurately representing Earth.
Identify one map projection commonly used for general world maps and explain how it compromises distortions to create a balanced representation.
The Robinson projection is commonly used for world maps because it balances distortions in shape, area, distance, and direction. Unlike the Mercator projection, which exaggerates size near the poles, or the Peters projection, which distorts shape, the Robinson projection minimizes extreme distortions to create a visually appealing and practical map. While it does not perfectly preserve any single spatial property, it provides a more proportionate and realistic depiction of the Earth. Because of its balance, the Robinson projection is widely used in textbooks, classrooms, and general reference maps, making it one of the most recognizable world map projections.
