The Mercator and Other Projections
For a long time, map-makers have struggled with one central problem. Maps are flat (2D), but the world is round (3D). How could their maps ever be accurate? They lose a whole dimension! Well, in reality, no map is totally accurate. Each one distorts the Earth somehow, because of how they’re made. The process of making maps is called projection. We project Earth’s surface onto a 2D map.
The world as seen through the Mercator Projection.
Every world map you’ve ever seen is inaccurate (unless it was a globe). And I don’t just mean imperfect. Maps have some pretty serious flaws! Each one distorts the world considerably. Just take a look at the map above. The southernmost continent, Antarctica, looks enormous. In reality, South America is a lot bigger. The map is just distorted around the north and south poles.
And why is it distorted like this? Well, because we’re flattening a 3D surface into a 2D one. This inevitably distorts some of the shapes. Think about what would happen if you did that with, say, a soccer ball. Even if you cut it open and re-assembled the pieces, you could not make an accurate rectangular map. You can actually try this with something less valuable, like an orange. Although, you’ll get the same result.
The Earth isn’t flat. But, we have to flatten it to map it out.
In fact, map projections are really only useful where they do not distort the Earth. Each one distorts different locations, making them useful in unique ways. We’ll look at a few of them next to demonstrate this point.
Map Projection Types
Cylindrical map projections are the most widely used map projections. Their name comes from how they’re made. It’s kind of a strange process which we use a computer to do. Basically, we put the Earth in a cylinder and then blow it up (like a balloon). Once it fills the cylinder, it leaves its features as an imprint on the cylinder’s inner surface. Finally, we unroll this cylinder to make a 2D map.
If you roll up a map correctly, it forms a hollow cylinder.
This might seem like a strange way to make a map. But, it actually makes sense. As we expand the Earth to fit our cylinder, it is inevitably distorted. Yet where is it least distorted? Near and around the center. Serious distortion doesn’t begin until we go far north or south. Fortunately, the majority of people live closer to the equator than the poles.
Our next map projection is the conic projection. Conic projections are made by projecting the Earth onto a cone. Basically, we repeat the cylinder method. But, instead of a cylinder, we use a cone.
Boy, it must be really loud in Antarctica!
Notably, this map projection is actually more accurate than the cylindrical projection. It distorts the Earth less overall. However, its distortions are more problematic. There’s almost no difference near the north pole, but the south is super stretched out. This is an issue because more people live south of the Equator than at the poles. Remember, cylindrical projections mostly distort the poles. As a result, they’re still more convenient than conic projections.
One last type of projection we’ll talk about is the interrupted projection. Interrupted projections are interesting in that they barely distort the Earth’s land. But to do this, they have to cut out some of the ocean.
Is it a map or a colorful orange peel?
An advantage of this map is that it allows us to see how big the continents really are. Africa is huge, and Australia much smaller. A disadvantage is that it is not useful for traveling. We still have to navigate over the blank areas!
What is the Mercator Projection?
The Mercator Projection is the most widely used map projection today. It is a type of cylindrical projection. Although, it’s different from most in that it’s built primarily for navigation.
Recall that cylindrical projections show more distortion as we reach the poles. Well, the Mercator projection is built so that this distortion is equal in all directions. If things expand as we go North, then they appear to expand to the East and West as well. This actually makes the overall distortion larger.
Yet, it’s useful in that it keeps things uniform for navigation. If things became unevenly distorted, it would be hard to tell which direction we were going in. With the Mercator, only distance, not direction, is distorted. Another way to say this is that all measured angles remain accurate.