How to Construct and Interpret a Scale Map

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  • 0:01 A Scale Disaster
  • 1:38 How Scale Maps Work
  • 6:04 Creating a Scale Map
  • 8:39 Lesson Summary
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Lesson Transcript
Instructor: Paul Brege

Paul has been teaching middle school science for the last 10 years, and has his bachelors degree in Elementary Education.

This lesson will explain what a scale map is and how it represents two different things on the map expressed as a ratio. This lesson will also demonstrate the steps needed to create a scale map from any ordinary map.

A Scale Disaster

Once there was a king who needed to build a stable for his daughter's new horse. She had recently outgrown the pony she had been given as a child and needed a proper steed. To keep the gift a surprise, the king hid the new horse and had a stable made from measurements he took himself. Heel-to-toe, he walked out the distance. The stable was to be 20 steps long and 10 steps wide. He sent his best carpenter the measurements to have a stable built at the castle in preparations for the gift.

But when the princess noticed a new stable being built, she was sad because it was a small stable, and she had truly hoped for a larger horse. This stable was only big enough for another small pony. When the time came and the horse was finally brought out of hiding, the princess was instantly glad again, realizing it was much bigger than the pony she already had.

The king was confused and asked the carpenter what had happened. That was when he noticed the carpenter's small feet. The measurements from the king had been made with his much larger foot, and the stable had been built by the carpenter with tiny little feet. The carpenter set at once to make a larger stable.

While this story may seem childish, it actually conveys a very interesting point. How big are things when we measure them? For instance, when you look at a map, things are much smaller and closer together than we know they actually are. If the map only showed that grandma's house is three inches away, then why does it take nine hours to get there?

This lesson will focus on something called a scale map, how to read them and how to make your own.

How Scale Maps Work

Scale map

Typically, scale maps work like this: in the corner of the map, there will be something called a scale. A scale is actually just a ratio of two numbers. So, a scale map is just a map that contains a scale on it. Pretty simple, huh?

The first number relates to the map. The second is the corresponding place that the map actually portrays. The ratio will look something like this: 1:18,000. The way you read this is 1 to 18,000. You can think of it as saying one of something on the map is equal to 18,000 of that exact same thing in the real location. A scale map takes one item and tells how many of the same item would be needed in the real world to make the actual distance.

This is different from something called a bar scale, which is a line on the bottom of some maps that shows a distance on that particular map.

Bar scale

For example, if we look back at our map, this means that one of anything placed on the map is equivalent to 18,000 of the same thing in real life. So if I tell you the distance on the map from A to B is one inch, we can start making some headway.

Distance between points A and B

From what we already know about scale, that means that the true distance from A to B must actually measure 18,000 inches in real life. Remember that 1:18,000 means that 1 inch on the map is actually 18,000 inches in real life.

However, since we don't normally measure large distances with such a small unit, it would be a bit like using a tiny ruler to measure the distance to your neighboring city. But we can convert these units into something more recognizable. If you were to divide 18,000 by 12, that would be how many feet it represents instead of inches because there are 12 inches in a foot. This would be 1,500 feet; a more manageable number.

The scale is still the same, 1:18,000, but you could also say that 1 inch on this map is equal to 1,500 feet, which is really still the same as 18,000 inches. You do this type of conversion all the time when you tell someone how tall you are in feet instead of inches. If you were 66 inches tall, you would also be 5 feet, 6 inches high. Both numbers are the same height; you just converted to different units.

Oh, I want to demonstrate the best part of this type of map. You don't even have to have a special tool to measure how long something is! You can use anything to measure with, maybe you have a pen or an old shoelace laying around. You can even measure with things like your hands. It works like this. New picture, please!

This map has two locations that are labeled C and D.

Example map

Say your pinkie finger was the exact distance from point C on the map to point D.

Measuring distance with finger

Because this is a scale map, (and our scale is 1:18,000) that would mean that in real life, the distance from point C to point D would really be 18,000 of your pinkies lined up end-to-end.

When using objects to measure, the measurement must be consistent.

Another way to say this is that you would take 18,000 of this same pinkie to cross the lake and cover the distance between point C and point D.

I understand that this would be an insane amount of pinkies, but it would totally work. Now, like the king from the story, you need to keep the same measurements the whole time; you can't swap out pinkies mid project. One of your pinkies might be close in length to a friend's pinkie, but I bet they aren't the exact same. Remember, the great part about this type of map is that you can use anything as your measuring tool. Go tell your friend to find their own cool measurement!

Even if the story about the king was meant for a younger audience, can you see how these ideas are related? The king was using his foot to measure length, but the carpenter did not have the same sized shoe, so when he measured for the stable, the size was different and things got all messed up. Can you imagine trying to cram that horse into a pony-sized stable? That would be quite a trick.

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