Map Projection & Scale

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  • 0:01 What Is a Map Projection?
  • 1:31 Maps and Scale
  • 2:47 Lesson Summary
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Lesson Transcript
Instructor: David Wood

David has taught Honors Physics, AP Physics, IB Physics and general science courses. He has a Masters in Education, and a Bachelors in Physics.

After watching this video, you will be able to explain what a map projection is, what a map scale is, and why they need to be carefully chosen when creating a map. A short quiz will follow.

What is a Map Projection?

The Earth is spherical. Or to be more exact, it's a vertically squashed sphere. But humans often like things to be flat, and that can be a problem. If you want to really see what the Earth looks like, you need a globe.

Whenever we create a flat map, it isn't really an exact depiction of the surface of the Earth because the surface of the Earth isn't flat at all. A flat map is a projection. A map projection is a way of representing the surface of a celestial sphere on a flat surface.

The problem with a map projection is that they are never entirely accurate. It is impossible to take the peal of an orange and flatten it out without first cutting it apart. So, in the same way, you can't unwrap the surface of the Earth and put it on a piece of paper. And this means you have to make choices about what you'll sacrifice to make it flat. Maybe things at the top and bottom of the map will look bigger than they really are. Or maybe it won't be as accurate when measuring distances left to right. Some map projections are useful in some situations, while others are useful in others.

Most modern world maps use a projection called the Mercator projection. The drawback of this projection is that things near the poles appear too big, and things near the equator appear too small. So, for example, Greenland and Antarctica aren't really as big as they appear, and Northern Africa and South America are much bigger than they appear.

Maps and Scale

The issues in the different types of map projections are issues of scale. When you look at a map, there is a scale. A scale tells you the ratio of a distance on the map to the actual distance in real life. For example, a scale of 25,000:1 tells you that every one inch on a map will be 25,000 inches in real life or every one centimeter on the map will be 25,000 centimeters in real life. On a map, a scale looks like this.

The problem with a map projection is that the scale is not consistent. One centimeter on a map projection is different in different areas of the map, and this is what creates its limitations. Technically all maps are projections because the Earth is curved everywhere. But on small scales, like maps of towns or local areas, the scale is so similar across the map that you don't really need to worry about it. Only at larger scales does it produce the huge anomalies we've been talking about.

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