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Saturday, March 19, 2011

What's the Best Projection?

See National
As geographers -- especially geographers who travel with a giant globe -- we are often asked this question. What kind of map, people want to know, will eliminate distortion?

Because the earth is nearly spherical in shape, a globe is the only way to represent it without distorting shape, area, distance, and/or direction. Any effort to preserve one of these four properties will require a loss in one or more of the others. Therefore, the "best" projection will vary, depending upon which of these characteristics is most important. As a guide for sailing a ship, direction is extremely important, for example. Unfortunately, the projection that best achieves this -- the Mercator -- has become one of the most popular for world maps, even though it grossly distorts area, shape, and distance! is the online version
 of the official National Atlas of the US,
first printed in 1874.
The National Atlas article Map Projections: From Spherical Earth to Flat Map is the best place to start learning about the trade-offs among the various projections. Further detail is provided by the U.S. Geological Survey article Map Projections, which includes a series of tables that identifies the suitability of various projections according to the properties preserved, the scale at which each is appropriate, and the appropriate use of each. Both the National Atlas and USGS articles include helpful glossaries, and describes the trade-offs that apply to globes, as well as to flat maps.

EarthView is nearly unique (duique, as Dr. Hayes-Bohanan says, because there are two of these special globes in the world), so its advantages and disadvantages differ from ordinary globes. Compared to most ordinary globes, EarthView:

  • has a much larger scale, and therefore more detail
  • has a much larger scale, but still not nearly as detailed as a typical highway or city map
  • is hand-painted, so features are more vivid
  • is hand-painted, which introduced a few small errors (ask the team where they are!)
  • is hand-painted, so it has to be treated with extra care
  • is very tall, so much of the northern hemisphere is hard to see from outside
  • is very tall, so some things are best understood from a distance
  • is very tall, so it does not fit in most classrooms or homes
  • is not round on the bottom, so Antarctica is flattened (and is not visible from the outside)
  • has a zipper on the International Date Line, which is just cool
  • has three air holes in the top, and a fan on the side -- also cool
  • rests on the South Pole, so it does not properly show the tilt of the Earth's axis
  • can be viewed from inside, so the entire planet is visible at the same time (except whatever is right behind your head)
  • can be viewed from inside, so that east appears on the left and west on the right (north is still up, though)
  • can be viewed from inside, so it looks like stained glass (see Mapparium in Boston for a globe made of real stained glass)
  • is a physical globe -- whereas most ordinary globes are combined physical/political -- so country boundaries are not visible (except island nations, of course)
One of the most noticeable differences between EarthView and other maps and globes is that in EarthView (or outside of EarthView) we can more clearly see that the Pacific Ocean is full of islands -- many of them inhabited. For example, French Polynesia is an "overseas collectivity" of France with over 100 islands and nearly 300,000 people, and is just one of many clusters of archipelagos in the vast Pacific Ocean.

The comparative visibility of Pacific Islands is a function of both projection and scale. On many flat maps of the world, the Atlantic Ocean is centered, with the Pacific pushed to the edges. On both maps and globes, a typical Pacific Island -- if shown to scale -- is comparable in size to the dot of a letter i, and therefore very difficult to represent. Even on EarthView, some artistic license has been used to make the islands more visible. Though the islands themselves are drawn to scale, the shallow waters around them generally appear much larger than would be proportional.

Learn more about the Pacific islands from two previous posts on this blog -- A Vast Ocean and Survivor Islands. We also recommend the interactive Map South Pacific site for finding maps of specific regions and archipelagos and the CIA's Oceania map (PDF format) for an overview.

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