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Octahedral map

By David Shaw, 27 June 2017

Time to create a map! Making a map of the entire Earth is tricky, because paper is flat, and planets are curved. There are lots of different ways to ‘flatten’ Earth, and each way produces a different shaped map. This method is super spiky as it involves triangles.

You will need

• Globe of Earth
• 8 paper equilateral triangles
• Pencil
• Eraser
• Thin, good quality masking tape

What to do

1. Although it’s easier to use tape during this activity, it may damage the globe. If the globe isn’t your own, seek permission before using tape on the surface. Before you start, do a test to check. Stick a small piece of tape on a ‘blank’ section of the globe, such as the southern Indian Ocean. See what happens when you gently remove the tape. If you’re worried about damaging the globe, do this activity without tape – just use your imagination!
2. The next few steps divide Earth into triangles. Start by running a strip of masking tape around the equator.
3. Next, mark out four right angles at the North Pole. Run strips of masking tape all the way south along the lines of longitude until you get to the South Pole.
4. Look at your globe. The surface is now divided up into eight sections, each with three corners. They’re kind of like triangles, but on a round surface.
5. Take a triangle of paper and look carefully at one of the sections. Try to draw the section accurately in the triangle. It’s tricky because the triangle of paper and the ‘triangle’ on the globe are actually different shapes, but give it a go!
6. Choose another section and copy it too. Keep copying sections until you have a copy of all eight sections.
7. Assemble your world map out of the eight triangles you drew. There are many different ways you can put them together.

What’s happening?

Making maps is a challenge. Although the ground looks flat, it’s actually curved. That means the only accurate maps of the whole Earth are globes!

Of course, having a flat map is very useful. So people have developed lots of different ways to make flat maps of Earth. These are known as ‘projections’ because they project the sphere of Earth onto a flat surface.

Most online maps use the Mercator projection, which is very good at keeping countries the same shape. However, it makes countries near the equator look smaller than they really are, and areas near the poles are much bigger.

The Gall-Peters projection is a popular alternative. It’s an equal-area projection, which means every country is the right area. Unfortunately, it’s not good at preserving shapes. Countries near the equator are stretched up and down, and areas near the poles are squished.

This map is known as an octahedral map. It’s based on a shape called the octahedron, which has eight triangular faces. This map is pretty good at preserving both shapes and areas. But it leaves gaps in the map and depending on how you put the pieces together, it might be hard to see which direction is north.

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