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M
aps, of course, are an essential tool for geographers. While the AP Human Geography course is not a course in cartography [the discipline of map-making], there are some essential things to know about the way maps are made and how they are effectively used. It will eventually be more important that you understand how to use maps, but that skill will be improved by knowing a bit about how maps are made.
The first thing to know is that all maps are distortions; they cannot capture the full meaning of what they try to represent; and the smaller the scale of the map, the greater the distortion. Small scale maps show large land areas on various paper sizes. Large scale maps show small land areas on various paper sizes. A small scale map, for example, might be as small as 1:100,000,000, or 1 cm on this paper represents 100,000,000 cm in the real world.
Already, I've referred to one of the essential features of a map [its scale], so let's begin with this: there are five parts to almost all maps.
Maps Have Five Essential Components
- Title. Simple enough, all maps should/must give a short description that says what the map is about; that's its title.
- Legend. A legend [or a map key] tells the user what symbols, shaded areas, colors, lines, and other features of the map mean.
- Scale. A map's scale is a ratio or a fraction that says this: one length on this map represents another [usually much larger] length in real life. For example, a map of South Florida would have to show an area about 50 miles on each side—but it needs to do so on a reasonably small piece of paper, say 18" by 18". In this case, lets use obvious measures: 18" of paper needs to represent 50 miles in real life, so 50 miles is 3,168,000
inches—and 1 inch on the map represents 176,000 inches in real life [3,168,000÷ 18 = 176,000]. Since a map's scale is a ratio, or a fraction, in our example, the scale would be 1:176,000 or 1/176,000.
Maps are often referred to by the relative size of their scale. Our example, by comparison to a world map, is a large scale map. To depict the entire world on that same 18" sheet of paper, we would need to use a much, much smaller scale, something on the order of 1:88,000,000.
- a ratio of 1:10,000 means that the size of objects on the map is 1/10,000 of its size in real life
- a ratio of 1:5,000,000 means that the size of objects on the map is 1/5,000,000 of its size in real life
- a ratio of 1:100,000,000 means that the size of objects on the map is 1/100,000,000 of its size in real life
- 1/10,000 is a larger fraction than 1/5,000,000, so the 1:10,000 is the larger-scale map of the two
- when referring to a map by its scale, you are merely expressing whether the fraction used is large or small
- Indexing grid. An indexing grid is a system of absolute reference. On world maps, and maps of world regions or countries, the indexing grid will usually be the lines of latitude and longitude, centered by the equator and the prime meridian. On larger scale maps, such as a city map or a map of a national park, the indexing grid may also use lines of latitude and longitude, but frequently may use a system of reference based on margins that are numbered and lettered.
- Orientation. On most maps, this is simply the answer to "which way is north"? A map of a shopping mall or a theme park, however, often say something like "you are here".
Projections
Cartogrpahers use projections to prepare maps. Think of the process like this: take a globe, place a source of light inside and project the image on a wall. This is a good way to picture how a narrow slice of the globe can be mapped. To depict the entire world, think of that same globe wrapped with a cylinder of light sensitive paper. Either way, the result will be distorted.
Mercator Projection
This map is probably the most familiar map of the world, its called a Mercator Projection, so named for its creator, Gerardus Mercator, who was born in Flanders [making him 'Flemish'], which is today part of the modern state of Belgium. It is also the oldest [1569] and most distorted of all of the world maps you'll encounter in the AP Human Geography course.
Transverse Mercator Projection
Mercator projections are precisely accurate along the tangent line, typically the Equator, but increasingly distorted as the distance north or south of the Equator increases. Look for example at Greenland on the map above and below. The map below is a "transverse" Mercator projection that uses the 90W° line of longitude as its central meridian. In real life, Greenland's landmass is much better represented on the transverse Mercator. So why is the Mercator still one of the most widely used maps? Well, partly because it was the first: its shapes are familiar to many people. The second is that the Mercator is the only world map projection where straight lines [called rhumb lines] are lines of constant compass bearing and can be used in all directions and remain true for all lengths. This is why the Mercator was created in the first place: its a navigation map. If a navigator draws a straight line from Miami to Lisbon, Portugal and measures its angle, the ship will arrive at its destination if the crew makes sure to keep the same compass direction the whole way across the ocean. That cannot be said of any of the other maps below.
Robinson Projection
The Robinson Projection map was prepared to correct some of the distortions of the Mercator Projection. The strength of the Robinson projection is that it preserves depicting the entire planet on a single contiguous plane, so that the relative location of the world's landmasses are approximately correct. Its weakness is that directions and areas are not true anywhere but along the Equator. It was designed to "look right" at the expense of precision: neither directions or landmass sizes are preserved.
Sinusoidal Projection
Comparing the Sinusoidal Projection to the Robinson and Mercator reveals a subtle difference and a very large problem. The subtle difference is that the Sinusoidal Projection shows all areas [meaning the size of the indexing grid] equal in size, but not equal in shape. The very large problem is that it is not contiguous.
Orthographic Projection
The Orthographic Projection is a further compromise, it makes no attempt to depict the entire surface of the Earth, rather it shows what the Earth would look like from the perspective of someone very, very far away, such as on the Moon. It does, however, show why airline flights from Chicago to China do not fly west, but rather fly north.
The Polar Route
This final image is from the wikipedia entry on the so-called "Polar Routes" flown by major airlines over time. On the far left, the shaded areas are the former Soviet Union and its satellite countries called the Eastern Bloc. Airlines could not fly over these areas so, they had to deviate from the most efficient route: a "great circle route" over the north polar region and devise other routes. After the collapse of the Soviet Union in 1991, cooperation with the Russian government has led to the use of a number of flights over the north pole between destinations in North America and Eurasia. Fewer destination cities in the Southern hemisphere mean fewer flights over the southern polar region.
If you're interested, here's the URL to the entry [//en.wikipedia.org/wiki/Polar_route]. There are a number of things in the entry that pertain to intergovernmental cooperation, something of concern in Topic 4.
Note: All images are from the United States Geological Survey [USGS] except the Polar Airline Routes map, which is from Wikipedia.
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