Mittwoch, 29. Januar 2014

World Maps 9 Projections and propaganda

Mercator does have its advantages, of course. It’s perfect for wayfinding; it’s the only projection for which straight lines on the map represent constant directions on the earth’s surface. If point A is directly below point B on the map, then point A is due south of point B. But Mercator’s distortions make it less than ideal for studying geography.

The trouble with Mercator

Because Mercator misrepresents the true areas of nations and continents, it can lead to misunderstanding — intentional or unintentional. Here are two ways that Mercator promoted particular political interests in the second half of the twentieth century.

The Cold War

During the Cold War, maps of “us” and “them” were often drawn to emphasize the threat represented by the USSR and its allies. The Mercator projection was the perfect choice for anti-communist cartographers: because the USSR was at such high latitudes, Mercator stretches it out of proportion to its true size. In the map below, the Warsaw Pact nations become a sprawling red menace:
Figure 10-1. Map of the world, drawn using Mercator projection, with Warsaw Pact nations shaded red.
map (Mercator projection) of Warsaw Pact nations
Redrawn in Robinson projection — a popular compromise between equal-area and conformal mapping — the USSR becomes a little less menacing.
Figure 10-2. Redrawn in Robinson projection.
Warsaw pact nations (Robinson projection)
Now redraw it again in the Peters equal-area projection, and the USSR shrinks to its true size.
Figure 10-3. Redrawn in Peters equal-area projection.
Warsaw pact nations (Peters projection)
Suppose you were a U.S. voter in 1960. Which of these would be most likely to make you support an increase in military spending?
If that didn’t convince you, cartographers could always offer a new perspective, as Time’s cartographer, R. M. Chapin, did in 1952:
Figure 10-4. “Europe from Moscow.” Map by R. M. Chapin, Jr., in Time, March 10, 1952.
Europe from Moscow (map)
From this perspective, it’s easy to imagine (red) armies sweeping across Western Europe.

North and South

One reason that Mercator wasn’t replaced sooner is that its distortions make the world’s most powerful nations appear larger, while poorer nations nearer the equator shrink. By the middle of the twentieth century, many people were pointing out that the Mercator projection made the powerful “North” appear more important than the poorer “South” and thus shaped people’s attitudes — albeit unconsciously — about the world.
How bad is this misrepresentation? Europe, at 3.8 million square miles, is made to appear larger than South America at 6.9 million square miles. Africa is the second-largest continent (after Asia), but in the Mercator projection, it looks about as big as Greenland, which in reality is one-fourteenth Africa’s size.
People who imagine Africa or South America as small will tend to underestimate not only the importance of those continents, but also their diversity. Many Americans think of “Africa” as a single place. In fact it encompasses a tremendous variety of cultures, ecosystems, and climatic regions; Africans speak more than 2,000 languages, and there is more genetic diversity among Africans than in all the rest of the world. Treating Africa as a cultural and political monolith would be absurd — and dangerous in an era of increasing globalization.

The Peters projection

To correct the misconceptions promoted by the Mercator projection, Arno Peters, German map maker, historian and journalist, popularized an equal-area map projection in the early 1970s. Equal-area projections weren’t new, but the time was right, as African nations were winning their independence from colonial powers and many Europeans and Americans were growing weary of the Cold War.
The Peters projection, like Mercator’s, is cylindrical, but it compresses the map near the poles, preserving the map’s rectangular appearance but making the relative areas of any two regions on the map proportional to their relative areas on the globe.
Figure 10-5. The world in Mercator projection.
map of the world in Mercator projection
Figure 10-6. A cylindrical-equal area projection.
map of the world in cylindrical equal-area projection
The Peters projection received a fair amount of criticism. Conservatives charged that it amounted to propaganda, and in fact it was used most often in a deliberate effort to change people’s perceptions of the globe — though, of course, to correct misperceptions created by earlier maps.
A more practical problem is that the Peters projection distorts the shape of the continents far more than Mercator, especially near the poles, so that Canada and Russia appear to have been run through a wringer. All cylindrical projections stretch out the regions near the poles; a cylindrical equal-area projection compensates for that not by removing that distortion but by adding a second one. As a result, it isn’t a particularly elegant solution to the problem of accurately portraying the world. It does, however, maintain the familiar (if completely inaccurate) rectangular outline of the Mercator map.

Improvements and compromises

There are equal-area projections that don’t as badly distort the shapes of the continents, but they require giving up the rectangular map outline. The Mollweide projection, for example, is frequently used when accurately representing area is more important than describing shape — to show global distribution of populations or goods, for example.
Figure 10-7. The Mollweide projection is an equal-area projection that doesn’t distort shape as badly as the Peters projection.
Mollweide projection
The maps most used today in textbooks, magazines, and newspapers are compromises. Since 1998, National Geographic has used the Winkel Tripel projection — which is the average of two other projections — to show the whole earth.
Figure 10-8. The Winkel Tripel projection, developed in 1921, is the arithmetic mean of the equirectangular projection and the Aitoff modified azimuthal projection.
Winkel Tripel projection

The right projection for the job

When you’re reading a map, then, it’s important to be aware of the projection. What aspects of the map are represented accurately, and which are distorted — and are those choices appropriate to what’s being communicated? Remember, just as there is no perfect projection, there aren’t necessarily any bad ones, either — just bad uses of them.
The Mercator projection, for example, has been revived in recent years to meet the needs of digital mapping. Equal-area maps are great for looking at the entire globe, but for street-level maps, you can’t beat Mercator, in which a straight line always represents a consistent direction and a rectangular building will appear as a rectangle. And for street maps, Mercator’s distortions are usually negligible. But if you want to “zoom out” to a global view — as Google Maps lets you do — you’ll have to maintain the same projection all the way through. For Google Maps, then, the only choice was Mercator.

Keine Kommentare:

Kommentar posten