Geography For Dummies. Jerry T. Mitchell

Чтение книги онлайн.

СКАЧАТЬ

      Telling the truth, but telling it skewed

It’s certainly true that geography seeks to provide accurate information about Earth. It’s also true that flat maps are inaccurate and therefore counterproductive to the pursuit of truth — at least in a limited sense. But the four disadvantages of globes are so serious that geographers prefer dispensing with honesty (globes) and using flat maps even though they lie. Indeed, those disadvantages of globes may be recast as advantages of flat maps:

       Unlimited field of view: You can show as much or as little of Earth as you want on a flat map.

       Low cost: Flat maps cost much less than globes. In fact, a good-sized atlas containing hundreds of maps may cost less than a single globe.

       Accommodates detail: Want to show a small area in great detail? Not a problem on a flat map.

       Efficient data storage: You can fold up a flat map and put it in your pocket. Or you can put the equivalent of a hundred globes in a single atlas and carry it in your hand or stick it in your backpack. Or you can search online via your smart phone for a map of about just any place you want. That’s better than trying to carry 100 globes, right?

      

The bottom line is that it’s okay if flat maps lie, as long as you know you are being lied to and understand the nature of the lie.

Different Strokes for Different Folks: A World of Projections

      If you are a veteran map-gawker, you know that all world maps don’t look the same. And if you’re not, then look again at Figures 4-2 and 4-3. Figure 4-2 looks something like a rectangle, shows the entire Earth, and is centered on the intersection of the Equator and Prime Meridian. Figure 4-3 is a circle, shows only the Northern Hemisphere, and is centered on the North Pole. As mentioned earlier, the two maps offer contrasts with respect to the ways maps lie: distance, direction, shape, and size.

      The appearances in the maps differ because of different kinds of projections. That is, the maps are products of different methods of transferring the curved globe to a flat surface. Over the years, cartographers have developed literally dozens of different projections. Most maps are accurate and/or visually pleasing in some respects, although inaccurate or visually displeasing in other respects.

      

At this point, you may feel like saying, “Look, Jerry, why don’t you spare me the details? Just tell me which projection is the best one so we can move on to the next chapter.” I wish it were that simple; I really do. But the simple fact is that a winning projection doesn’t exist. Every projection has good points and bad points. The trick is to know the pluses and minuses of particular projections so that choosing the best map for specific purposes is easier. It really is a case of different strokes for different folks, or at least different projections for specific situations.

If you’re starting to think that this is a somewhat arcane field of study, well, you’re right. As a new geographer, you don’t need to commit map projections to memory. (I know several professors of geography who don’t go near this stuff!) What is important, however, is that you appreciate the variety and complexity of map projections and understand that even though all flat maps lie, some do a pretty good job of showing all or part of Earth.

      All in the (map) family

Generally speaking, map projections belong to one of three families: azimuthal, cylindrical, and conic (see Figure 4-4).

       Azimuthal (or planar): A flat piece of paper (or plane, hence planar) is placed against the globe. The globe is then projected onto the flat paper, rendering a flat map.

       Cylindrical: A paper cylinder is placed over a globe. The globe is projected onto the paper. The cylinder is then cut vertically and unwrapped from the globe, yielding a flat map of the world.

       Conical: A conical paper hat is placed on the globe. The portion of the globe under the hat is projected onto the paper. The paper is cut in a straight line from its edge to the tip of the cone. The cone is then opened up and put down flat.

      (© John Wiley & Sons Inc.)

      FIGURE 4-4: Families of map projections.

This reminds me to remind you that the process of projection does not literally involve projecting a globe onto a flat surface. Instead, mathematical formulas are used to plot the locations of lines (latitude, longitude, continental boundaries, and so on) on maps. Thanks to satellite imagery, you can now check the accuracy of your work in a way that was never possible before.

      Five noteworthy liars

      

Here are five rather well-known projections that represent the range of formats shown in Figure 4-4. There will not be a test over this. I repeat, there will not be a test. So don’t try to memorize this stuff, but instead, just sort of let the maps visually soak in to give you an appreciation of the variety of projections that are available.

      The Mercator projection

Gerhard Kremer, who’s much better known by his adopted Latin name, Gerardus Mercator, developed the Mercator projection in 1569. This cylindrical projection (see Figure 4-5) is easily the most famous world map of all time. Mercator crafted his projection to aid navigation, and in that regard, the map is a gem. Straight lines on this map correspond to true compass bearings so a navigator could use it to plot an accurate course. This achievement was a very big deal in the late 16th century, and by the middle of the 17th century, a majority of Western European navigators swore by this map.

      (© John Wiley & Sons Inc.)

      FIGURE 4-5: The Mercator projection.

Because of its seafaring fame, the Mercator Projection later came into widespread use as a general-purpose map. That is, it found its way into classrooms as wall maps and into books and atlases. It became more or less the official world map, which is unfortunate because, although the shapes of landmasses are fairly accurate, the projection is extremely distorted with respect to size.

      Notice that the lines of longitude on the Mercator projection don’t meet at the Poles, as is the case in reality. Instead, the map shows the lines of longitude as parallel lines. This means that the North and South Polar regions have been stretched and become lines (the top and bottom borders of the map) that are as long as the Equator — 25,000 miles. One result is that land areas become disproportionately enlarged the closer they are to the areas of maximum distortion — the Poles. Alaska and Greenland are good examples. Alaska appears much larger than Mexico, while Greenland appears much larger than the Arabian Peninsula. In reality, Mexico is larger than Alaska, and the СКАЧАТЬ