Are these maps of Africa optical illusions?

[standingwave]

Originally Posted by Michael63129

Is 22,000 miles considered to be close, since that was taken from a geostationary satellite? If so, how far do you have to be before viewing angle effects become insignificant (e.g. Moon)?

You will always have the distortion that the objects closer to the hortizon/tangent point will be foreshortened but setting that aside, how high to have to get to see an entire hemisphere? The answer is infinitely high as it's an arctan function of the satellite's height wrt the radius of the Earth. I would say that after 10 Earth radii (5 Earth diameters), you're definitely into the area of diminishing returns.

[whc.03grady]

Originally Posted by For You

Is it possible to peel an orange (apple, whatever) in such a way that what you have ends up completely flat?

If it was, we wouldn't be having this conversation.

[2square4u]

Originally Posted by Acsenray

Is there any digitized Mercator that automatically morphs the map as you move the center point?

Garmin's Mapsource program (with World Map installed) does this. Don't know about anything online, though, but you could try looking for demo maps on Garmin's website.

[Maastricht]

...believing their country was the biggest and therefore most important one!

Oh, NOW I get it. Funny, I come from a country that is very small (the size of Massachusets) but still plays, well, B league. As Dutch, we have a vested interest in not caring about the size of our country. Instead, we are proud of how such a small area of land still accomplishes that much.

As an attitde, I recommend it to whomever shares the feeling quoted in the OP. " Damn, we're one third the size of Africa. Now look at their acccomplishments, and then at ours. 'nuff said. "

Of course, an even better attitude would be: "Damn, Africa is that big and apparently so underdeveloped and badly organized? Hmm, lets look at the opportunities and possibilities..."

For me personally, Africa is where the hungy little kids live that make me feel guilty all the time. I don't like that Africa was even bigger then I thought, mainly because that means that there are even more of those starving little kids. Yes, I'm irrational and I don't know much about the contemporary demographic trends.

[Darth Panda]

Originally Posted by Darth Panda

Goode Homolosine for the win

http://en.wikipedia.org/wiki/Goode_h...ine_projection

Originally Posted by For You

Is it possible to peel an orange (apple, whatever) in such a way that what you have ends up completely flat?

Originally Posted by whc.03grady

If it was, we wouldn't be having this conversation.

Check out my link to Goode - it's about as close as you'll get.

[Chronos]

Quoth standingwave:

You will always have the distortion that the objects closer to the hortizon/tangent point will be foreshortened but setting that aside, how high to have to get to see an entire hemisphere? The answer is infinitely high...

Actually, no: About half a lightyear will do it, due to gravitational lensing. The formula is h = c²/2g, where c is the speed of light, and g is the surface gravity of the Earth.

[Mr Downtown]

Every projection—even Goode's homolosine—distorts something. Those interested in playing around with different projections to see the tradeoffs between angular, areal, and scale distortion should visit FlexProjector.com.

[Chronos]

Every projection—even Goode's homolosine—distorts something.

Well, yeah, interruptions are about as extreme a distortion as you can get. The virtue of Goode's homolosine isn't that it has less distortions, but that it concentrates the distortions mostly into regions that are usually of less interest, leaving less distortion for the regions that are of interest.

[Dr. Strangelove]

Originally Posted by Mr Downtown

The problems with Mercator projectors for general world maps is something that has been recognized for many decades, and Mercator schoolroom maps are actually pretty rare. That's why cartographers were so—ahem—Galled when Peters raised such a stink in the 1980s and why it seems odd to see this straw man trotted out so often.

The Mercator projection is, however, still used for applications such as Google Maps, and for a very good reason: it is the only rectangular projection that scales evenly in all directions. What this means is that you can zoom into any point, and have 1 mile north be the same number of pixels as 1 mile east (say). Of course, the actual scale for a given zoom level will vary based on distance from the equator. But for the most part we don't care about this since the variation is small when zoomed to a comfortable level (like city-sized or below).

[Baal Houtham]

Originally Posted by BACI

This image from space gives a pretty spectacular representation of the actual size of Africa...

Thanks for the pic. It may have been posted before, but I didn't see it. Michael63129 says it was taken from 22,000 miles up. It makes an interesting comparison for another posted picture of Africa from space, in which the continent appears much larger. I had some problems figuring out how high that picture was taken, and I had guessed 3 or 4 thousand miles -- a guess that was based on just holding a globe and looking at it with one eye shut.

That was puzzling because I didn't know why NASA would have satellites at that height. However a little research indicates that the image of big Africa was assembled as a collage from images taken by the Aqua and Terra satellites, from a little over 400 miles up.

Incidentally, looking with one eye at a globe indicates that four or five Earth diameters distance will come reasonably close to showing a hemisphere. So 40,000 miles up will put you in the approximate neighborhood. Which is about what standingwave said.

[Mr Downtown]

Originally Posted by Dr. Strangelove

The Mercator projection is, however, still used for applications such as Google Maps

Yes, and we cartographers gave Google a bit of poke about that at last year's conference. But not only is Web Mercator now the world's most popular projection by far, but Google Maps' scale levels have become a standard, used by Bing, Nokia, Esri, and even Open Street Map.