Earlier this month, United Nations member states voted nearly unanimously to encourage the use of maps “that more accurately reflect the true size of continents” in response to an African-led campaign raising awareness of the flaws of the Mercator map projection, the most widely used map in the world.
Liz Sutherland, GIS research scientist at the Canadian Severe Storms Laboratory, spoke with Western News to help untangle why the Mercator became the default, what the Equal Earth map does differently and why different maps are needed for different purposes.
Western News: What is the Mercator map? What was its purpose?
Liz Sutherland (LS): The Mercator Projection was invented in 1569 by Flemish cartographer Gerardus Mercator, who invented this revolutionary (at the time) world map to make it easier for ships to navigate the seas. It preserves a constant compass direction, or rhumb line, but grossly exaggerates the sizes of countries near the poles (not your fault, Mercator! Every map needs to distort something).
An example of a Mercator projection map (Strebe/Wikimedia Commons)
How did this map become the default for hundreds of years?
LS: It happened gradually. As maps moved from ships and navigation charts into classrooms, atlases, textbooks, newspapers and eventually digital mapping, we became accustomed to seeing the world presented this way. And once something becomes familiar, it can be difficult to question it. Many people trusted, or never really questioned the Mercator Map so it became somewhat difficult to show its flaws. The Mercator map outlived the original problem it was trying to solve – seafaring – and became embedded in our society.
Should we stop using the Mercator projection?
LS: Absolutely not! The Mercator projection is an incredibly useful projection for certain purposes, particularly navigation. The problem isn’t Mercator, the problem is using any projection without thinking about what you’re trying to represent. Unsure? Ask your local neighbourhood geographer! And if you want to learn more about maps and map projections, visit GIS Days on Nov. 18 a free, on campus open house exploring digital maps and mapping projects.
What is an equal-area projection map and how is it different from the Mercator map?
LS: In the world of cartography there are many categories of maps, each focuses on preserving a different quality such as area, distance, direction or shape. An equal-area projection is simply making a different choice than the Mercator (or conformal projections in general). Equal-area projections (maps like Equal Earth or the really cool Goode Homolosine or Mollweide) preserve relative size, or area, of features on Earth. But the decision to preserve area means the maps distort other properties – like distance or direction.
The Mercator Map Projection, which is part of a category of map projections called conformal projections, preserves local shape and direction, making them great for navigation, which is why we’ve used them so often historically.
Equal Earth map showing country boundaries (Wikimedia Commons)
Can you share examples of the size distortion seen in Mercator maps?
LS: One of my favourite ways to demonstrate this is with The True Size, which lets you move countries around the map and see how their apparent size changes with latitude.
The rule of thumb is that as you move towards the North or South poles, countries are going to distort more dramatically. Greenland is probably the most famous example, it looks comparable to Africa on a Mercator Projection, but in reality it can fit into Africa 14 times. Africa is the second largest continent in the world, though it doesn’t appear that way on a Mercator map.
The “Greenland effect” is prevalent elsewhere on the Mercator Map as well, Brazil is actually larger than the lower 48 states. Canada is also a great example. Because so much of our country extends into the high northern latitudes, the land area is substantially exaggerated.
How does this impact the way we think about the world?
LS: A map is the first place we’re introduced to the world and our place in it. It forms our own mental map, a perspective we carry with us into adulthood. When the same world map is shown to us over and over again, we naturally become familiar with its shapes, proportions and the relationships we see. We start to build our view of what the world “looks like” without seeing it.
That’s what makes map projections really interesting: a Mercator Map doesn’t intentionally tell us that countries near the equator are less important, but when we repeatedly see representations with certain places dramatically enlarged, it can influence our perception of the world around us.
Why can’t we make a map that’s perfectly accurate?
LS: The mathematical problem of flattening the earth is one massive, complex puzzle.
The fundamental problem here is that you can’t flatten a sphere without distorting it. And the Earth actually isn’t a perfect sphere. It’s an irregular, constantly changing shape that we model as an ellipsoid for mapping purposes.
Think about trying to peel an orange and lay the peel completely flat: you’ll have to stretch, tear, cut or otherwise alter it in order to make it work. The same thing happens when we make a map of the Earth. You can’t preserve everything perfectly at the same time. But that’s why we have hundreds of map projections! They’re all different solutions, and different tools work for different projects.
Are there other notable maps besides the Mercator and Equal Earth?
LS: There are hundreds of different map projections, and they can look wildly different depending on what they’re designed to do.
Anyone can visit the Western Libraries Map and Data Centre, including its Map Collection to see some of these maps in real life. There are some really beautiful and creative projections, some designed for very specific purposes.
A world map from the Nuremberg Chronicle, an illustrated encyclopedia combining religion, myth, history and science published in 1493. (Schedel, Hartmann, 1440-1514, cartographer)
And this is just the conversation about global map projections. Once you start working at a regional or local scale, the question changes again. For example, the projection I would use to map all of Canada might not be the projection I would choose to map Southwestern Ontario, and neither would necessarily be the best choice for mapping a small neighbourhood.
That’s one of the things I love about GIS: there isn’t one map projection that does everything. The projection you choose should depend on your data, your geographic area and what you’re trying to communicate.
Mercator and Equal Earth are really just the beginning of the conversation.
Learn more about how Western is navigating new realities.