Map Projections

Warm Up ► Draw an accurate map of South America with as many details as you can.

Warm Up ► Discuss with your teammate and write down 5 examples to the following questions: ► What are some uses of maps?

► Imagine a globe made of glass. Overlay pieces of silver in the shape of the landmasses. Now imagine a light at the globe’s center, casting land-shaped shadows in all directions. ► The cartographer’s job, roughly and poetically, is to gather those shadows and transform them into a reasonable portrait of the planet. ► This first, crucial step in mapmaking is called the projection. Projections fall into three basic categories: planar, conic, and cylindrical. Picking the right projection is crucial for achieving the map’s objective. planarconiccylindricalplanarconiccylindrical

Planar (Flat-Plane) Projection ► Project the Earth onto a plane that touches—or, technically, is tangent to—the globe at a single point, and you get a planar projection. ► Because this projection, also known as an azimuthal projection, is most accurate at its center, it is often used for maps focusing on one of the Poles.

Conic Projection ► Cap the globe with a cone to achieve a conic projection. Cut open the cone, and the basis of a map emerges. ► The map will be least distorted along the line where the cone touches the sphere. ► Conic projections are handy for portraying the United States, which fits nicely within the resulting smile-shaped map.

Cylindrical Projection ► Swaddle the globe and project its surface onto a cylinder. Slit the cylinder and flatten it into a map. ► This projection is most accurate near the Equator and greatly distorted near the Poles. ► The most famous cylindrical map is the Mercator projection, perfect for navigation but poor for teaching geography.

Cylindrical Projection ► Mercator Map

Pocket Globe?

Map Distortion ► Mapmakers tailor their creations to focus on area, shape, distance, direction, and other objectives. areashapedistancedirection areashapedistancedirection ► National Geographic continually refines the compromises involved in crafting a world reference map. world reference mapworld reference map ► Their objective chosen, cartographers rely on varied tools to accomplish it.

MAPS HAVE DISTORTION!! Some parts aren’t accurate, because the world is not flat.

Area ► To compare geographical data on a level playing field, pick a projection that maintains the correct proportions among the sizes of Earth’s landmasses. ► Such a map, often called an equal-area projection, would be useful to demographers. ► The price of getting the sizes right, however, is distortion in the shapes of the continents.

Shape ► Preserving the shape of a landmass—an important concern for those wanting to see what Earth “really” looks like—gets harder as the area covered gets larger. ► A world map can only preserve the continents’ shapes by distorting their sizes. Maps that stress shape are called conformal.

Distance ► Geometry students the world over learn that the shortest distance between two points is a line. Not on most maps. ► If distance is the focus of your map, choose a projection centered on a key point. Lines radiating from the middle will be equidistant. ► Shapes and sizes will be distorted, however, especially at the outer edges.

Direction ► Many navigational charts rely on projections focused on direction. Such maps, usually centered on one place, allow mariners to plot a journey they can actually sail without constant course corrections. ► That ability matters far more at sea than shapes and sizes, which can get distorted.

Putting It All Together ► National Geographic has wrestled for decades with the choice of a projection for reference maps of the world. In 1922 the Society adopted the Van der Grinten projection, which encloses the world in a circle. ► Their cartographers switched in 1988 to the Robinson projection, on which the high latitudes are less distorted in size (but more so in shape). A decade later, the Society began using the Winkel Tripel projection, which provides a better balance between size and shape

Robinson Projections ► a compromise map projection showing the poles as lines rather than points and more accurately portraying high latitude lands and water to land ratio

Interruptions Interruptions ► Only globes are edgeless. All other maps have to stop somewhere. Those unavoidable interruptions can actually help focus the map by drawing the reader’s eye toward—or away from—particular features. The projection seen here clearly focuses on land and would be helpful for mapping terrestrial data such as human population. Yet it distorts the sea, which covers 70 percent of the planet. All other maps have to stop somewhere. Those unavoidable interruptions can actually help focus the map by drawing the reader’s eye toward—or away from—particular features. The projection seen here clearly focuses on land and would be helpful for mapping terrestrial data such as human population. Yet it distorts the sea, which covers 70 percent of the planet.

The West Wing – Peters Projection