Understand different ways in which the Earth is represented on a two-dimensional space.
Maps are representations of the Earth's surface, but since the Earth is a three-dimensional sphere (or more precisely, an oblate spheroid), transferring its features onto a two-dimensional surface requires a mathematical transformation called a map projection. Every projection involves some trade-offs—whether in size (area), shape, distance, or direction—because it's impossible to perfectly preserve all these properties on a flat surface.
Understanding map projections is crucial for creating accurate and appropriate geographic visualizations, as the choice of projection can significantly affect how your data appears and is interpreted.
The fundamental challenge of map projections stems from topology: you cannot flatten a curved surface like Earth without introducing distortions. Think of trying to flatten an orange peel—you must either stretch some parts, compress others, or tear the surface.
Types of distortion:
No single projection can preserve all properties simultaneously, so each projection prioritizes certain characteristics while accepting distortions in others.
Equal-Area Projections preserve proportionality of areas across a map, ensuring that regions are accurately represented in size and making them particularly useful for comparing spatial distributions. In Mappica, you can choose from Conic Equal Area, Albers, Albers USA, Azimuthal Equal Area, and Equal Earth projections, which are all detailed below.
Conic Equal Area
The Conic Equal Area projection combines the advantages of preserving proportional area with the practicality of a conic layout. It achieves this by using two standard parallels to minimize distortion across a specific region. Distortion increases as you move farther from these parallels. The projection is a good fit for applications like environmental and agricultural mapping, especially for large east-west regions. In Mappica, the projection is set by default to use standard parallels of [0°,60°], which can be edited as needed.
Albers
The Albers projection, named after 19th-century German mathematician Heinrich Albers, is a specific implementation of the Conic Equal Area projection. Its defining feature is the preconfiguration of standard parallels in order to optimize the projection for Northern Hemisphere maps, and particularly those of the contiguous United States. In Mappica, these parallels are preset at [29.5°,45.5°]. The Albers projection is a classic choice for thematic maps that prioritize equal area; many cartographers rely on this projection to ensure geographic areas are represented accurately in proportion to their true size, even when shapes are slightly distorted.
Albers USA
Albers USA is a customized adaptation of the standard Albers Equal Area Conic projection designed for U.S.-focused maps. It uses the Albers projection for the contiguous United States while insetting Alaska and Hawaii in the lower left corner to present all 50 states in a compact and visually coherent layout. This projection is frequently employed in thematic maps, such as election maps, where accurate area representation and the inclusion of all states are essential.
Azimuthal Equal Area
The Azimuthal Equal Area projection represents the Earth on a flat plane while preserving the true proportional area of all regions. The projection provides a circular layout when centered on a pole or a specific point, with minimal distortion at the central point and increasing shape and angular distortion radially outward. This makes it particularly effective for mapping polar regions, hemispheres, or specific continents. Widely used in scientific studies, it is ideal for applications like biodiversity mapping, climate research, or global environmental analyses where accurate representation of area is important.
Equal Earth
The Equal Earth projection is an equal-area projection designed to represent the Earth's landmasses proportionally while maintaining an aesthetically pleasing and familiar appearance. Developed in 2018 by Bojan Šavrič, Tom Patterson, and Bernhard Jenny, it builds upon the Robinson projection but ensures true area representation, making it ideal for thematic and environmental maps. The projection's smooth curves and well-balanced proportions minimize distortion of both shape and scale, especially near the equator and mid-latitudes, while distortion increases gradually near the poles. The Equal Earth projection is widely used for global maps where maintaining accurate area relationships is critical without compromising visual clarity.
Conformal projections preserve shapes locally by maintaining angular relationships, ensuring that angles and directions are represented accurately. This makes them ideal for navigation and for mapping where local shape accuracy is critical. In Mappica, you can choose from Mercator, Transverse Mercator, Conic Conformal, and Stereographic projections, which are detailed below.
Mercator
The Mercator projection preserves local angles and shapes, making it conformal, but it produces significant area distortions, which increase with distance from the equator and become extreme near the poles.
Developed by Gerardus Mercator in 1569, the Mercator projection is one of the most influential map designs in history. Its ability to represent loxodromes (straight-line navigation paths) made it invaluable for maritime and aviation charts. However, its severe area distortion—especially near the poles—limits its suitability for representing global distributions. Despite this, the Mercator projection remains widely used in modern web mapping platforms, such as Google Maps, where preserving accurate angular relationships at the local level is prioritized over representing areas proportionally at the global scale.
Transverse Mercator
A variation of the Mercator projection, the Transverse Mercator focuses on narrow vertical strips of the Earth, preserving local shapes and angles (conformal properties) across the entire map. Distortion of distance and scale is minimized along a central meridian.
The projection is the foundation of the Universal Transverse Mercator system, which divides the globe into 60 zones, each 6° wide, for precise regional mapping. Widely used in surveying, engineering, and military applications, the Transverse Mercator is helpful for projects requiring detailed topographic accuracy, particularly in regions with limited longitudinal extent.
Conic Conformal
The Conic Conformal projection is widely used for regional maps in mid-latitude areas such as the United States or Europe. It preserves angular relationships and local shape accuracy, making it ideal for topographic and aeronautical charts. Distortion is minimized along the standard parallels, while the central meridian serves as a reference for aligning the projection. With straight meridians and curved parallels, this projection provides practical accuracy for regional navigation and geographic analysis. In Mappica, the projection is set by default to use standard parallels of [30°,30°], which can be adjusted as needed.
Stereographic
The Stereographic projection preserves angular relationships and accurately represents shapes in localized areas, making it a conformal projection. Distortion is minimal near the central point of the projection, from which distortion increases radially. The central meridian serves as an axis of symmetry. This projection is particularly effective for mapping polar regions, where it minimizes distortion near the poles. Its circular format has also been historically applied to other specialized uses, such as small-scale regional maps and, in astronomy, celestial maps.
These projections prioritize maintaining accurate distances from specific points or along specific lines, making them ideal for practical applications like aviation or communications. In Mappica, you can choose from Azimuthal Equidistant and Conic Equidistant projections, which are detailed below.
Azimuthal Equidistant
The Azimuthal Equidistant projection preserves accurate distances along straight lines radiating outward from a central point. This makes it especially useful for maps displaying flight paths, communication ranges, or disaster response zones. Its circular layout emphasizes connectivity and reach, allowing users to visualize how different locations relate to the central point. While it distorts shapes and areas away from the center, this projection is an essential tool for understanding distance-dependent phenomena.
Conic Equidistant
The Conic Equidistant projection offers accurate distance measurements along all meridians and selected standard parallels, making it well-suited for large-scale regional maps. This projection is commonly used for applications such as transportation or planning maps, where maintaining proportional distances along specific reference lines is critical for accuracy.
Cylindrical projections map the Earth's surface onto a rectangular grid, with straight, parallel meridians and parallels. In Mappica, the Equirectangular projection is the only true cylindrical projection, while the Natural Earth projection is pseudo-cylindrical, with curved meridians to balance distortion.
Equirectangular
The Equirectangular projection maps latitude and longitude as a uniform grid, with meridians and parallels forming straight, equally spaced, perpendicular lines. This structure makes it a true cylindrical projection, as the Earth's surface is effectively "unwrapped" onto a rectangular plane with a linear mapping of geographic coordinates. While it heavily distorts shapes and areas, especially near the poles, its simplicity and regularity means it is commonly used in various digital applications, raster-based maps, and other scenarios where maintaining a consistent, grid-like structure is more important than geographic accuracy.
Natural Earth
The Natural Earth projection is a pseudo-cylindrical projection designed for global maps, offering a visually appealing balance of shape, area, and distance distortions. Unlike true cylindrical projections, its meridians are gently curved, except for the central meridian, which remains straight. This design minimizes distortion near the equator while reducing the extreme stretching of polar regions common in cylindrical projections. The Natural Earth projection is often used for thematic world maps where visual clarity and aesthetic appeal are prioritized over strict geographic precision.
Consider your data's geographic extent:
Consider your analysis type:
Consider your audience:
Web Mercator (EPSG:3857)
Adaptive Projections
In Mappica:
Best Practices:
Understanding map projections helps ensure your geographic visualizations accurately represent spatial relationships and support valid data interpretation. The right projection choice depends on balancing the needs of your analysis, your data's characteristics, and your audience's requirements.