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Map Projections: Mercator, Gnomonic & Conic

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  • 0:02 Map Projections
  • 0:43 Mercator
  • 2:13 Gnomonic
  • 3:12 Conic
  • 3:48 Lesson Summary
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Lesson Transcript
Instructor: Jessica Whittemore

Jessica has taught junior high history and college seminar courses. She has a master's degree in education.

This lesson will explain and illustrate the Mercator, gnomonic, and conic map projections. In doing this, it will highlight the strengths and flaws of each while also defining the term 'cartographer'.

Map Projections

When making world maps, cartographers, or mapmakers, have their hands full. After all, figuring out how to portray our spherical Earth on a flat piece of paper definitely presents some challenges. In today's lesson, we'll take a look at these challenges as we discuss three of the most commonly used map projections: the Mercator, the gnomonic, and the conic.

Now, in order to understand these projections, we're going to have to get a bit creative. We're going to pretend it's Christmas and the Earth is a basketball we're trying to wrap. Although this sounds absurd, it'll help us understand the different projections. Since the Mercator is the projection most of us are familiar with, we'll start with it.

Mercator

To illustrate the Mercator projection, we're going to wrap our basketball with striped paper. However, we're not going to finish the job. Instead of wrapping it tightly, we're going to leave the edges of our paper open. This will form a cylinder around the ball. Now, since this cylinder remains unwrinkled, the lines of our paper stay perfectly parallel.

Mercator projection illustration
basketball wrapped in paper

Now, let's take this image and bring it back to the real world. When a cartographer creates a map using the Mercator projection, it's like they take the globe and wrap their maps around it like a cylinder. For this reason, Mercator projections are often referred to as cylindrical maps.

Now, just like the lines on our wrapping paper remained straight, the Mercator projection allows cartographers to draw parallel lines of latitude and longitude. These lines make the Mercator projection invaluable for navigation because they make it possible to label any point on the globe. Since this is the kind of map most of us are used to, I remember this one by saying, 'the Mercator is the main projection.'

Of course, the Mercator projection has some flaws, the main one being it distorts areas closest to the poles. Going back to our basketball, imagine what it would look like if we tried to finish our wrapping job. We'd have to sort-of stretch the ends of our paper to make it cover the whole ball. In the same manner, the Mercator projection stretches the areas closest to the poles. This causes a distortion in size, making places like Greenland look way bigger than they really are.

Gnomonic

Our next projection is the gnomonic projection. Speaking rather officially, the gnomonic projection projects points from a globe onto a piece of paper that touches the globe at a single point. To remember this one, we just have to remember that 'mon' means 'one,' as in MONocle or one person controlling a MONopoly.

Now let's get back to our basketball. To illustrate the gnomonic projection, we're going to use paper decorated with lines and circles radiating from one point. However, we're not going to wrap the ball. We're just going to lay it on the ball like this:

Gnomonic projection illustration
basketball with lines radiating

As odd as this might seem, this is how cartographers project the globe to give us the gnomonic projection. Since this one projects from one single point, it lets cartographers create circle routes for those who use these maps. These circle routes are used by pilots who fly the skies. Of course, this one also has some flaws, the main one being it distorts distances between points.

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