Mercator projection is the display of a map of the world onto a cylinder in a way where all of the parallels of latitude have the same length as the equator. This method is useful for specific climatological maps and marine charts because it creates a display that offers features that are easier to read for the average person.
This map option is named after the Flemish cartographer and geographer who invented it in 1569. Gerardus Mercator made a significant portion of his income by selling celestial and terrestrial globes. For more than 60 years, his work was considered the finest in the world. Many of his innovations are still used in mapmaking today, and there are several excellent examples of his work that have survived through the years.
The design is useful for navigators because the ship can sail in a constant compass direction to reach its destination. That eliminates the course corrections that are often prone to errors. There are several pros and cons of the Mercator project to consider; however, which is why this map is not the preferred option for general-purpose needs.
List of the Pros of Mercator Projection
1. It is easier to plot courses on a Mercator projection.
The Mercator projection makes it easier to navigate over long distances on our planet because of two properties: straight rhumb lines and conformality. That means the courses and bearings that must be set are measured using protractors or wind roses, making it much easier to transfer directions from point-to-point on the map. All you need is a pair of navigational protractor triangles and a parallel ruler to determine where you need to be going.
2. This method ensures that angles and shapes stay true.
Because the Mercator projection is a conformal one, the shapes and angles within any small area are essentially true. Even though there is some distortion on the map, you’ll have that issue on almost any visual navigational device. Imagine trying to create an accurate display on an orange peel and you’ll have an idea of what it takes for cartographers to create something realistic. This advantage makes it possible to navigate around tricky land formations from a sailing point of view to ensure accuracy with each course plot simultaneously.
This design was the first that could preserve the 90-degree angles that occur when the vertical and horizontal lines come together on the map. That means latitude and longitude remain pure even if there is a visual “stretching” of the world as one moves away from the equator.
3. Distortions don’t occur when zooming in with a large map.
When you use a digital version of a Mercator projection, then you won’t see the same distortions when you zoom in on a specific location as you would with other maps. That means it is an excellent option for viewing or navigating through small cities or regions because you have an accurate representation of what to expect. The pixels in that small area will have a constant scale to the real world at all times on the vertical and horizontal access. That’s why this option is a good choice for street maps. The only time when you’ll notice the distortion is when you start to zoom out.
4. All cylindrical projections, meridians, and parallels are straight and perpendicular to one another.
The Mercator projection ensures that all of the lines on the map are straight and perpendicular to one another, making it the only one where each primary direction remains true even though our planet isn’t flat. The stretching of the map increases when moving north and south, but that also means the east-west scale remains the same as the other, preserving an accurate shape for the various continents even if there is some distortion of their size. All lines of constant bearing receive representations by straight segments to make it easier to transfer information when it becomes necessary.
5. It is useful for street mapping services.
Most of the major online street mapping services that you’ll find on the Internet today use a variant of this system for their images. Even though Google moved away from using it some in recent years, Bing, MapQuest, Yahoo!, and OpenStreetMap use some version of this technology to present small-scale items at a readable level for users. This advantage is possible because the distortion levels remain mathematically constant with the way that Mercator designed this projection almost five centuries ago.
6. This option provides a higher level of certainty in directional use.
There are some rightful criticisms of the Mercator projection in that it distorts some of the areas of the planet to make them seem more important than others to the casual observer. It is also the only map that provides an almost unerring certainty in navigational needs. Even Christopher Columbus took advantage of this benefit when he sailed from Europe to reach the New World. That means the information is more readily available to travel correctly without constant recalculations to ensure one is on the correct path.
7. It provides tangible information.
The Mercator projection provides tangible information that is usable to the casual observer. Whether you use one of the older paper versions or a digital copy, it offers data that you can see and touch. That means you’re connecting with the planet in a meaningful way because you’re having a tangible experience with the representation. Having feelings of physicality when plotting a course makes the entire experience more real, which leads to better accuracy over time.
8. Most people can access a Mercator projection without charge.
The average person uses a Mercator projection almost all of the time, even if they do not realize that is what they’re doing. When you go online to check your directions or look up data about a specific city, then you are using an updated version of this planetary representation. If you want a paper map, then this tangible representation is quite affordable as well. You can even purchase some of the original maps from Mercator in the 16th century for less than $300 in some situations. It is one of the most affordable ways to get to know more about our world today while offering everyone the advantage of positional awareness.
List of the Cons of Mercator Projection
1. It forces the map to create a distortion away from the equator.
Linear scale is constant on a Mercator projection in every direction, preserving the shapes and angles of small objects effectively. This fulfills the conditions of a conformal map projection. The side effect of this outcome creates the disadvantage of inflating the size of objects that are away from the equator. It begins infinitesimally but then accelerates with latitude until it becomes infinite at the poles. That means the landmasses appear far larger than they actually are compared to the continents of Africa or South America.
2. Its usefulness is limited in the polar regions of the planet.
The Mercator projection becomes undefined at the north and south poles. Since you can navigate around the top of the arctic circle, the map becomes useless because you would need to go off the map to come back onto it. That makes its useless when you must navigate through those two regions of the planet. Even though the lines offer the benefit of constant direction, your limitations on certain trips would require you to carry multiple projections to ensure you were navigating in the correct direction.
If you want to have a map of Antarctica, then the Mercator projection is unable to accommodate that need. You’d need to choose one of the other map options that are available right now.
3. You cannot compare the area of landmasses with a Mercator projection.
If you have a Mercator projection to use as a map, then the information it provides you is not useful for the comparison of the area of the continents. This disadvantage can apply to the oceans as well since the waters near the poles encounter the same distortion that the landmasses experience. When the scale increases, then the more significant the changes to the distortion will be. That issue can lead to the misperception that some areas of the planet are smaller or bigger than they actually are. Unless you know about the properties of this design, a casual observer would think that Greenland is literally the same size as all of Africa.
4. It makes Europe and North America seem more important.
An international treaty in 1884 set the prime meridian on our planet as the line of longitude that is 0° through the former Greenwich Observatory in the United Kingdom. This agreement is the reason why most world maps actually place the prime meridian at the center of the map, leading to the perception that the “developed” continents and countries are more important or central to our planet’s existence when compared to the other options that are available on the market today.
5. The distortions make it impossible to see the true layout of the planetary surface.
Because this projection exaggerates the areas that are further from the equator, there are some distinctive changes that must be taken into account when observing this information. Russia appears to be four times the size of the United States when using this method even though it is only about twice the size instead. Alaska takes up as much room on the map as Brazil does, but the country is five times larger than the state.
Outside of the issues at 70° that make this map essentially worthless, you’ll find that Ellesmere Island on the northern end of Canada’s Arctic archipelago looks to be about the same size as Australia even though it is actually 39 times smaller than the only country/continent combination in the world today.
Is a Mercator Projection a Good Map to Use?
As with most cartography efforts, there are times when a Mercator projection would be the best choice to use. There are also circumstances where almost any other style of map would be a better choice.
There are several different map styles that we can use today to know about where we are in the world or how to get to where we want to be. Although the scale approaches infinity when approaching the poles, the pros and cons of a Mercator projection show that it is one of the most accurate methods of staying true to navigational needs in the world today. That’s why this option will soon be celebrating its 500th anniversary of use.
Natalie Regoli is a child of God, devoted wife, and mother of two boys. She has a Master's Degree in Law from The University of Texas. Natalie has been published in several national journals and has been practicing law for 18 years.