Map Projections for Different Purposes: Navigation, Area, and Distance

Choosing the right map projection is one of the most important decisions in cartography. A projection that is perfect for oceanic navigation would be misleading for a population density map, and a projection designed for classroom wall maps would be useless for plotting a flight path.

Introduction

Professional cartographers, GIS analysts, and map designers select projections based on the specific purpose of each map. Understanding which projection to use for which purpose is a fundamental skill in geographic information science and critical for anyone who works with spatial data.

Navigation Maps

• Recommended: Mercator (marine), Lambert Conformal Conic (air)
• Key Property: Conformal (preserves angles)
• Reason: Compass bearings must be accurate

Navigation maps must preserve angles because navigators need to read compass bearings directly from the map. The Mercator projection is the standard for nautical charts because a straight line on the map represents a constant compass bearing (rhumb line), allowing sailors to simply follow a heading.

Aviation charts typically use the Lambert conformal conic projection because it covers mid-latitude regions with excellent shape and angle accuracy. Great circle routes, the shortest paths between two points, appear as nearly straight lines on this projection, simplifying flight planning.

Thematic and Data Maps

• Recommended: Mollweide, Albers Equal-Area Conic, Equal Earth
• Key Property: Equal-area (preserves relative size)
• Reason: Visual area comparison must be accurate

Thematic maps displaying data like population density, GDP per capita, or rainfall must use equal-area projections. If the map inflates high-latitude regions like the Mercator does, sparsely populated areas like Greenland and northern Canada receive disproportionate visual weight, distorting the data story.

The Mollweide is popular for global thematic data. For regional maps, the Albers equal-area conic is the standard for the contiguous United States. The Equal Earth projection, introduced in 2018, was designed specifically as a modern equal-area alternative that maintains pleasing aesthetics.

General Reference Maps

• Recommended: Winkel Tripel, Robinson, Natural Earth
• Key Property: Compromise (balances all distortions)
• Reason: Overall visual accuracy for education

General reference maps intended for education, atlases, or wall display benefit most from compromise projections that avoid extreme distortion of any single property. The Winkel Tripel and Robinson projections are the most popular choices, with the Natural Earth projection gaining ground as a newer alternative.

These projections ensure that viewers get a reasonably accurate impression of both the sizes and shapes of countries without the dramatic distortions that conformal or equal-area projections introduce. They are not ideal for any technical purpose but excel at giving a balanced overview.

Distance Measurement Maps

• Recommended: Azimuthal Equidistant, Two-Point Equidistant
• Key Property: Equidistant (preserves distance from center)
• Reason: True distance from a specific location

When the primary purpose is to show distances from a specific location, the azimuthal equidistant projection is the best choice. It shows the true distance from the center point to every other point on the map. This is commonly used by ham radio operators, seismologists, and for range-circle maps.

The two-point equidistant projection preserves distances from two specific points rather than one, which can be useful for showing travel distances between two cities to all destinations. However, this projection distorts shapes and areas more than single-point equidistant maps.

Web and Digital Maps

• Recommended: Web Mercator (EPSG:3857)
• Key Property: Conformal, tileable
• Reason: Mathematical simplicity for tiled web maps

Almost all web mapping platforms use Web Mercator (EPSG:3857) because its mathematical properties make it ideal for the tiled architecture of digital maps. Each zoom level divides the world into square tiles that can be loaded independently, and the conformal property ensures that streets and buildings look correct at any zoom level.

The dominance of Web Mercator in digital mapping means that billions of people primarily view the world through this lens. While the distortions are negligible at street level, they become pronounced at continental and global scales. Some digital platforms now offer alternative projections for zoomed-out views.

Key Facts

• Navigation maps must be conformal to preserve accurate compass bearings.
• Thematic data maps must be equal-area to prevent visual bias in data representation.
• General reference maps benefit from compromise projections like Winkel Tripel.
• Web maps use Web Mercator because it tiles efficiently into square grid cells.
• No single projection is best for all purposes; the right choice depends on the map's goal.

Fun Facts

• The US Geological Survey uses over a dozen different projections across its map products.
• The Equal Earth projection was introduced in 2018 specifically as an aesthetic equal-area alternative.
• Some GIS software includes over 100 projection options for analysts to choose from.
• Choosing the wrong projection for a data map can make the data appear to tell the opposite story.

Final Thoughts

Matching the right projection to the right purpose is both a science and an art. Understanding the trade-offs between conformal, equal-area, equidistant, and compromise projections empowers mapmakers and map readers alike to create and interpret maps more accurately and honestly.