Map Projections Explained: How the Earth Is Represented on a Map

Why Are Map Projections Necessary?

Have you ever tried to lay an orange peel flat on a table without tearing it? It's impossible. The peel bends, tears, or forms wrinkles. The very same problem arises whenever we try to represent the Earth on a flat surface.

No matter how carefully you try, the peel can never be flattened completely without tearing, folding, or becoming distorted. This is because the surface of an orange is curved, whereas the table is perfectly flat.

Exactly the same thing happens with the Earth.

Our planet has a curved surface, while a map or a computer screen is flat. To represent the world on a map, it is therefore necessary to apply a mathematical transformation that converts the Earth's surface into a two-dimensional representation.

This transformation is called a map projection.

What Is a Map Projection?

A map projection is a set of mathematical rules that makes it possible to transform the position of points on the Earth's surface into coordinates that can be used on a flat surface, such as a paper map or a computer screen.

Every point on the Earth is represented on the map using precise mathematical formulas. The result is a continuous and consistent representation of the territory, essential for drawing maps, planning routes, and displaying geographic data.

Coordinates always describe the same location on the Earth: only the way that location is represented on the map changes.

This transformation changes more than just the Earth's shape: it also changes how distances, areas, directions, and angles are represented. For this reason, choosing the right projection is one of the most important aspects of cartography.

Map projections are used almost everywhere: in GPS navigators, topographic maps, online services such as Google Maps and OpenStreetMap, GIS applications, and software such as OkMap.

Why Does Every Projection Introduce Distortion?

It may seem natural to ask why there isn't simply a "perfect" projection capable of representing the Earth without any errors.

The reason is purely geometric: a curved surface cannot be transformed into a flat plane while preserving all of its properties at the same time. This is a mathematical limitation, not a limitation of technology or measurement accuracy.

Every projection must therefore choose which characteristics to preserve most accurately and which ones to allow to be distorted. Some preserve angles faithfully, others preserve areas, and others preserve specific distances or directions.

As a result, there is no universally "best" projection. There is only the projection that is best suited to the purpose for which the map is created.

Example. On Mercator maps, Greenland appears enormous. Many people believe it is roughly the same size as Africa. In reality, Africa is about fourteen times larger. Greenland appears so large only because the projection progressively enlarges areas closer to the poles.

What Properties Can Be Preserved?

Since it is impossible to preserve everything simultaneously, every projection is designed to prioritize certain characteristics over others. The four most important properties are the following.

In the next chapter, we will see how these different priorities have led to the development of numerous families of map projections, each designed to meet different requirements.

The Main Families of Map Projections

Over the centuries, cartographers have developed undreds of different map projections, each designed to solve specific representation problems.

The various projections can be grouped into several major families, depending on the geometric surface used to project the Earth.

These surfaces should be thought of as geometric tools used to construct a map. In reality, there are no cylinders or cones surrounding the Earth: they are simply mathematical models that help transform a curved surface into a flat representation.

Cylindrical Projections

In cylindrical projections, the Earth's surface is represented as if it were projected onto a cylinder tangent or secant to the globe. After the projection, the cylinder is "unrolled" to produce a rectangular map.

Do not imagine a real cylinder or a real cone surrounding the Earth. They are geometric models used by mathematicians to construct map projections.

This family includes some of the best-known projections, such as the Mercator projection and the Web Mercator projection used by most online mapping services.

Distortion increases progressively as you move away from the equator, becoming very noticeable in the polar regions.

Conic Projections

Conic projections use a cone placed over the Earth. After the cone is unrolled onto a plane, the resulting maps are particularly accurate in the areas crossed by the standard parallel or standard parallels.

They are often used to represent continents or countries that extend primarily in an east-west direction, such as much of Europe and North America.

Azimuthal Projections

In azimuthal projections, the Earth's surface is projected directly onto a plane tangent to the globe at a specific point.

These projections are particularly effective for representing polar regions or limited areas around the point of tangency, where distortion remains relatively low.

Conformal, Equal-Area, Equidistant, and Compromise Projections

In addition to their geometric classification, map projections are also classified according to the property they preserve most effectively. In practice, this classification is the most important one when choosing which projection to use.

Compromise projections deserve a brief explanation. They do not attempt to preserve any single property perfectly. Instead, they distribute distortion in a balanced way. For this reason, they are often used for general-purpose maps.

The Most Commonly Used Map Projections

Over the centuries, hundreds of map projections have been developed, each designed to solve specific problems. In practice, however, only a few have become widely used and are now employed in GPS devices, mapping software, and online mapping services.

Understanding their main characteristics helps explain why the same geographic location can be represented in different ways and why every projection has its own advantages and limitations.

The Mercator Projection

Created in 1569 by the Flemish cartographer Gerardus Mercator, it is probably the most famous map projection in history. It is a conformal projection: it correctly preserves local angles and shapes, a characteristic that made it an essential tool for maritime navigation for centuries.

Its main limitation is the significant distortion of areas at high latitudes. As you move closer to the poles, continents and islands appear progressively larger than they actually are.

A well-known example is Greenland, which on traditional Mercator maps appears to be comparable in size to Africa. In reality, Africa is about fourteen times larger.

Web Mercator

Whenever you use Google Maps, OpenStreetMap, Bing Maps, or many other online mapping services, you are almost certainly viewing a map created using the Web Mercator projection.

Web Mercator is derived from the traditional Mercator projection, but it uses the WGS84 datum and a simplified mathematical formulation that allows tiled maps to be managed very efficiently. This approach makes it possible to load map tiles quickly while zooming and panning.

The widespread adoption of Web Mercator is not due to its absolute accuracy, but to the simplicity with which it enables the creation and distribution of digital maps on a global scale.

UTM (Universal Transverse Mercator)

The UTM system deserves special attention because it is often mistaken for a simple map projection.

In reality, UTM is a coordinate system based on the Transverse Mercator projection. The Earth's surface is divided into 60 zones, each 6 degrees of longitude wide, and each zone uses its own projection to minimize distortion.

This subdivision provides highly accurate metric coordinates and makes UTM one of the most widely used systems in technical cartography, topographic surveying, hiking, and GPS receivers.

It is precisely because each zone covers a limited area that distortion remains low, allowing highly accurate distance measurements and cartographic calculations.

A hiker crossing the boundary between two zones naturally remains at the same location on Earth, but the UTM coordinates change.

Lambert Conformal Conic

The Lambert Conformal Conic projection is one of the most widely used conic projections. It preserves angles and local shapes over small areas and is particularly well suited for representing regions that extend mainly in an east-west direction.

For this reason, it is used by many national mapping agencies and cartographic organizations, especially in mid-latitude regions.

How to Choose the Most Suitable Projection

There is no single answer that fits every situation. The choice of projection depends on the type of work to be carried out, the size of the area to be represented, and the property you want to preserve.

Mapping software such as OkMap automatically handles a wide range of coordinate reference systems and map projections, allowing you to work with data from different sources without having to deal with the complex mathematical calculations that make these transformations possible.

Why Does Google Maps Use Web Mercator?

At this point, you might wonder: if Web Mercator introduces distortion, why is it used by Google Maps, OpenStreetMap, Bing Maps, and most other online mapping services?

The answer is simple: because it offers an excellent compromise between simplicity, speed, and compatibility.

Web Mercator makes it possible to divide the Earth's entire surface into millions of small square tiles. Each zoom level uses tiles of the same size, which can be loaded quickly only when needed.

Thanks to this approach, you can pan and zoom smoothly without having to download the entire world map every time. This is one of the main reasons for the success of modern online mapping services.

For many applications, the accuracy provided by Web Mercator is more than sufficient. When accurate geodetic measurements are required, it is preferable to use coordinate systems and algorithms specifically designed for that purpose.

Google Maps was not designed to be a school atlas, but a fast and convenient mapping tool.

Map Projections in OkMap

OkMap supports a wide variety of coordinate reference systems and map projections, allowing you to import, display, and process data from different sources without having to perform complex coordinate transformations manually.

The software uses the information contained in coordinate reference systems (CRSs) and their associated EPSG codes to automatically transform coordinates, raster maps, GPX tracks, waypoints, and other geographic data while maintaining consistency across different formats. For example, EPSG:4326 identifies the WGS84 geographic coordinate system, while EPSG:3857 identifies the Web Mercator projection used by most online maps.

This makes it possible, for example, to overlay a georeferenced map, a GPS track recorded in the field, and data from online mapping services, even when they use different coordinate reference systems.

Understanding the role of map projections helps you interpret these results correctly and choose, whenever necessary, the coordinate reference system that best suits your work.