I'm wondering why this maps uses an orthographic projection, resulting in 3 maps to view the whole world. What were the requirements or the reasons to choose this projection (why not Mercator ) ?
this map maps the plastic distribution in the oceans
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2Orthographic projections do not preserve shape, area, or distance, but it has a natural appearance and is often used for illustrations.– Mapperz ♦Commented Jul 18, 2014 at 0:01
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1Jamie Hawk made these maps. You can ask National Geographic yourself using this email address: [email protected].– FezterCommented Jul 18, 2014 at 1:30
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2 Answers
Orthographic projection is able to show the poles, which mercator can not do.
Furthermore, the projection looks like the view from outer space, which feels kind of natural. It only shows half of the worlds surface, but that's what you see from outer space.
An even more "natural" view would have resulted from a perspective projection, which looks like the view from an orbiting vehicle (near space) but covering slightly less ground/ocean.
The Mercator projection, is a conformal map projection so any angles measured on the map are the same as if measured on the globe. It also has the property that all straight lines on the map represent loxodromes, or lines of constant azimuth. Those are useful properties in surveying and navigation.
Beyond that, however -- and especially when mapping very large regions -- Mercator is extremely overused as a projection. It is inappropriate due to the extreme distortions in sizes of countries found far away from the equator (or other contact line).
Andre explained why they used an orthographic projection, but they could have used several others depending on the overall message, style or feel they wished to convey.