Flattening Earth
#gisWithKids - Introduction to map projections
On a paper map, or many maps on computers, Earth is shown as flat. But as people have known for thousands of years, Earth is round! (That's why we have globes.) Yet we often use flat paper maps and see flat maps on the computer, and flat maps can be easier to work with for some tasks, like seeing all of the continents at once.
So how do we turn something round into something flat?
(Click the arrow on the right of the image below to scroll and explore flattening an orange, then keep scrolling down to learn more.)
A map projection allows us to turn the round Earth (or orange) into a flat surface. Calculations (math equations) determine where each point on Earth would be on the new, flat surface, and each spot on the globe has a unique spot on the flat surface. That means that for any point on the flat map, we can figure out where it came from on the round surface of Earth.
As you noticed with your orange, you can't just take something round and make it flat without changing the shape. Like with your orange, you introduced a number of tears in the peel. And you might have noticed the peel wrinkle as you tried to push it flat.
When we make the round orange (or Earth) flat, we can't keep it the same shape. We have to change something about it.
Changes to the shape are called distortions - and projections can distort (or change) a number of things about Earth when it is shown on a flat map:
- Sizes of things as compared to each other on the map, and the shape of things -- Did you stretch or squish your orange peel to get it flat?
- Distances between things -- Did you tear your orange peel to flatten it?
- The direction you'd go to get from one place to another -- Any places on your orange peel that used to be up and are now somewhere else? Look at where the dot from the stem and the bottom are now.
Different projections have different distortions. When you are making a map, you need to think about what the map is for and what you are willing to distort (or change). If your map is to show the size of places, pick a projection that keeps the sizes compared to each other the same.
Fun projections
There are an infinite number of ways to turn the round Earth into a flat surface, but here are some fun ones to explore.
Remember all these maps are interactive, so click, zoom, pan, and explore the world in the different projections!
Mercator projection
A lot of maps you'll see on the wall use the Mercator projection. It was made for navigation around the globe!
Be careful though! It doesn't show the right shape or size of the continents. Look at North America and Africa. Which one is bigger?
While they look close in size here, Africa is really about 23% (almost a quarter) bigger than North America.
Add circles
One way to see the distortion is to look at circles on the map. Click the button below to stamp the same circle all over the map.
Wait I said add circles, and all the same! You say they are the same size? What is going on?
Well, each point on the circle is 750 miles from its center. But because of the projection, their shapes are distorted and they don't look the same. This is what happens to the land, too.
When to use this projection
If you are making maps for navigation at sea, this is a good projection to choose. It's a bad choice when making a map to compare places. (These same statements apply for a variant on this projection, Web Mercator, which is [unfortunately] standard for interactive maps on the internet.)
Robinson projection
With the Robinson projection you see a bit of a different shape.
While visually pleasing, it does have all types of distortion (distance, shape, area, direction). Near the equator the areas are more true to size.
Tip: Look at some of the rectangular states (like North Dakota) to see how they are affected.
Add circles
Let's add circles again to see the distortion. Click the button below to stamp the same circle all over the map.
When to use this projection
This is a good choice if you are making a general world map.
Cube projection
The Cube projection is called that because you could fold this into a cube-shaped globe.
Folding into a cube - from ArcGIS Pro help .
This projection also has all types of distortions but distances are correct along the equator.
Tip: Looking for some distortion to explore?
Add circles
Time to add circles to see the distortion! Click the button below to stamp the same circle all over the map.
Look how some circles are cut and the pieces are on other edges, and how pointed the circles near the poles are.
When to use this projection
While a fun shape, it's not a great projection for storytelling with maps (other than to fold them).
Berghaus star projection
The Berghaus star projection sure has a fun shape! This projection correctly shows some distances and directions in the center, but not shapes or areas.
Don't forget to explore the map! Click and pan --->
Add circles
How do 750 mile circles look when added to a star? Click the button below to stamp the same circle all over the map.
Check near the edges. What distortion do you see?
Bonne projection
My daughter likes how the Bonne projection looks like a heart!
While it has a unique shape, this projection actually shows the correct sizes (areas) of the land. But the shapes, distances, and direction are all distorted.
While its area is correct, the shape of Australia probably isn't what you picture.
Add circles
What does a circle near Australia look like? Click the button below to stamp the same circle all over the map.
Does the circle's distortion (how it was pulled and stretched) match what you expected after seeing Australia?
Spilhaus projection
The Spilhaus projection became popular in 2018 for how it makes the oceans the focus of the map, presenting them as connected and realistically sized. It can be hard to orient yourself and see the land!
Fun fact: If printed on floor tiles, this map would let you create multiple Earth's covering your floor! The edges would line up correctly from one tile to the next.
Looking for an interesting spot to explore?
Add circles
Time to add 750 mile circles. Click the button below to stamp the same circle all over the map.
These circles have some interesting clusters (groups) and big size differences with nearby circles.
When to use this projection
This projection is great for maps focused on the oceans, especially looking at currents, flow, and patterns that cross them. Don't use it for comparing things, though.
There are so many ways we could flatten Earth into a paper map! While they are fun, remember why we need projections: they allow us to take a round object and represent it on a flat surface, or screen. Changing the shape has a cost, so as you pick a projection remember to think about if what you are changing is right for what you are showing with your map.
But sometimes, just explore and play with the projections, seeing what you can create.
What's next
To play with how circles look on some other projections, head over to Project ME! There you can pick a projection (many more than we looked at here) and then click "Static Buffers" to see how circles are distorted.
Or explore the following map - what appears like a sphere isn't always one. Can you see how it is different than a globe? (Hint: think about how much you see of Earth when a globe is still.)
Van der Grinten projection
Van der Grinten map with 750 mile circles
Oh you like the circles? Ok here you go, Van der Grinten with circles.
