C
Minutes and seconds that don’t tick away
On Earth’s surface, adjacent lines of latitude and longitude may be several miles apart, and that creates a potential problem if you wish to state the absolute location of a spot that is “between the lines.” For this reason, the graticule contains a couple of levels of refinement (see Figure 3-4).
(© John Wiley & Sons Inc.)
FIGURE 3-4: Degrees, minutes, and seconds.
First, the space between successive degree lines may be subdivided into 60 equidistant units called minutes ('). Second, the space between successive minute lines may be subdivided into 60 equidistant units called seconds ("). And if more exactitude is needed, then seconds may be carried out to as many decimal points as may be necessary.
Doesn’t this sound familiar? Sixty seconds in a minute? And for good reason. The system that you use to tell time goes back to the same Sumerian base-6 arithmetic that Hipparchus used to divide up a circle and also the world. Hmmm … there are 24 hours in a day. Think 24 being evenly divisible by 6 is just a coincidence? No way.
Chapter 4
Truthiness in Mapping
IN THIS CHAPTER
Imagine a million-dollar map contest. The only thing you have to do to win is to supply an exact map of the entire Earth that’s flat. Here’s how to enter!
1 Get your hands on a globe.
2 Peel off the surface layer in such a way that you end up with one big piece of map peel. (You may want to use somebody else’s globe because this procedure results in the globe’s complete ruin.)
3 Lay the map peel on a flat surface so that the two surfaces are completely in contact but without distorting the original map in any way. You can cut the map if you want, but pulling and stretching it is prohibited.
You are absolutely right if you think it’s going to be tough to submit a winning entry. Actually, it’s impossible. You can’t take a sphere-like surface (see the sidebar “Earth’s shape: Sphere-like, not spherical” for more on this), such as Earth, and lay it down flat without distorting the original image. This fact, however, hasn’t deterred people from making flat maps of the world or parts thereof. And, to do that, the mapmaker has to figuratively pull it here and stretch it there. The result is a map that’s full of distortion. Full of distortion? Well, simply put: Maps that lie flat lie!
EARTH’S SHAPE: SPHERE-LIKE, NOT SPHERICAL
People often say that Earth is a sphere. Not so. By definition, a sphere is a curved solid whose surface is always the same distance from its center, no matter at what point of the surface. Technically, Earth doesn’t fit that definition. Instead, Earth is an oblate spheroid, meaning it is somewhat flattened at its poles, or, if you prefer, it bulges somewhat around the Equator. The average distance from Earth’s center to the Equator is about 26 miles farther than the average distance from Earth’s center to the poles. Compared to the size of Earth, 26 miles isn’t a great distance, but it’s enough to make Earth not a real sphere. It’s better to say Earth is sphere-like, or an oblate spheroid.
Earth’s rotation causes its oblate-ness. The speed of Earth’s rotation is much faster at the Equator than near the Poles. This difference in speed may not be obvious, so think of it this way. Earth’s circumference measured along the Equator is about 25,000 miles. If you stand at a spot on the Equator for one day — for one full rotation — you’ll travel 25,000 miles. In contrast, if you stand a foot or two from the North Pole for one rotation, you’ll only travel a few yards. Obviously, somebody who travels 25,000 miles in one day is moving much faster than somebody who travels a few yards in the same time. So, the area near the Equator is spinning much faster than other parts of Earth. The outward, or centrifugal, force the high speed of rotation causes is so great that Earth bulges around the Equator as a result.
Maps of the world are among the most basic aids to geographic learning. Many people take it for granted that they are truthful. But in reality, all flat maps of the world lie — they simply cannot help it. If you’re new to thinking geographically, it is important that you appreciate that simple fact and understand the ways in which maps distort their portraits of your Earthly home. This chapter shows just how flat maps lie.
Seeing the Light: Map Projections
Accordingly, this chapter is about mapmaking with emphasis on the distortions that are inherent in flat maps of the world. But first, some basic vocabulary is in order. A map is a representation of all or part of Earth’s surface. Cartography is the field of mapmaking, and a cartographer is a person who makes maps. Way back when, cartography was pure freehand, and I do mean way back. The oldest known map is a 5,000-year-old clay tablet that shows physical features of Mesopotamia. Later, cartography became associated with instruments and techniques that most people think of as drafting. Nowadays, most cartography is done using a computer.
(© John Wiley & Sons Inc.)
FIGURE 4-1: Map projection.
