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Pangaea um?
January 30, 2013 11:47 PM   Subscribe

Just how badly does the Mercator projection distort our planet?
posted by special-k (49 comments total) 61 users marked this as a favorite

 
For those who might be confused, it works like a game where you take the red shapes of countries and drag them to where they should be, at which point it locks in and turns green. You win when they are all green.

This is awesome.
posted by Blasdelb at 11:55 PM on January 30, 2013


I'm done, although it did very definitely mess with my perceptions though. This is now one of my favourite cartography teaching aids, definitely best of the web.
posted by jaduncan at 11:59 PM on January 30, 2013 [5 favorites]


The best representation of the Earth is a globe! Failing that, I love the Dymaxion Map and the Cahill Butterfly map.
posted by the man of twists and turns at 11:59 PM on January 30, 2013 [3 favorites]


Failing that, I love the Dymaxion Map and the Cahill Butterfly map.

Obligatory XKCD.
posted by jaduncan at 12:06 AM on January 31, 2013 [14 favorites]


Yeah, but you can't do that. It's freaking me out.
posted by ApathyGirl at 12:11 AM on January 31, 2013 [18 favorites]


Cool!

It's not a game but a fun piece of software to play around with is NASA's G.Projector, which will take any arbitrary image file of the correct dimensions and recompute it between different map projections.
posted by XMLicious at 12:27 AM on January 31, 2013


I say this in every maps thread, since I've yet to actually see it: I really want to see a bog-standard mercator projection of earth, but not aligned like that. I want the poles arbitrarily placed (so instead of really stretched north and south poles at the top and bottom, why not put, say, madagascar along the top edge) and the projection then done as normal, distorting very different parts of the globe very differently to the same projection done aligned with our conventional latitude/longitude lines.

Why? I just think it'd be interesting, and cool.
posted by Dysk at 12:34 AM on January 31, 2013 [8 favorites]


I have one piece to go and I can't make it fit anywhere! THIS WILL HAUNT MY DREAMS.
posted by andraste at 1:49 AM on January 31, 2013


Oh hang on. There it goes. Now I can rest easy.
posted by andraste at 1:50 AM on January 31, 2013


Was it the Ukraine piece? Ukraine made me angry.
posted by saturday_morning at 1:54 AM on January 31, 2013 [4 favorites]


Greenland is still quite big, it seems, despite the Mercator bullshit.
posted by Jimbob at 2:23 AM on January 31, 2013 [1 favorite]


Okay, the point of the Mercator projection is simple. Navigation. On the Mercator projection, a rhumb line1 is a straight line. Rhumb lines are not great circles, but they're easy to hold course on -- you just set a bearing on the compass and hold it.

Mercator projections make this easy. Find your start point, find the end point, draw a straight line between them, measure the angle for your course, and assuming no currents, if you hold that course, you will get there. It won't be as short as a great circle, but in between 70°N and S, it'll be a decent approximation, and before we could determine longitude at sea, it was really the only reliable way to navigate the oceans -- so, Mercator created a map that made plotting courses by rhumb easy, despite the distortion that occurs as you near the poles.

It's not an accurate projection, and it's not even constant over the whole surface, but for navigation, it works very well indeed. Which is why nautical charts, to this day, remain Mercator projections. If you want a truly accurate projection, you must use a 3d shape -- an oblate spheroid. Anything that maps the surface of the Earth distorts either the shape of the landmasses, or the distance between them.



1 Rhumb line, a line that intersects each meridian of longitude at the same angle, or if you will, a straight course. If your course is 270° or 90° true, you follow a degenerate case called "a meridian of latitude", such as the Tropic of Capricorn or the Equator, if your course is 0° or 180° you follow a meridian of longitude, such as the Prime Meridian.

If you're at some other angle, you follow, on the glob, a curving course that would spiral into one of the pole, eventually.

posted by eriko at 2:36 AM on January 31, 2013 [28 favorites]


I say this in every maps thread, since I've yet to actually see it: I really want to see a bog-standard mercator projection of earth, but not aligned like that. I want the poles arbitrarily placed

Like these?
posted by vacapinta at 2:54 AM on January 31, 2013 [16 favorites]


Oh I get it now. Whew.
posted by trip and a half at 3:01 AM on January 31, 2013


(Whew because at first I thought it really was about pangaea.)
posted by trip and a half at 3:08 AM on January 31, 2013 [2 favorites]


Spoiler alert: completed puzzle (imgur link).

I don't know about anyone else, but I found the largest pieces the hardest. Which I guess is the point.

Protip: thanks to the vagaries of history and colonialism, a country with lots straight lines stands a good chance of being in Africa (and to a lesser extent the desert countries of the Middle East). Large states with very straight lines within countries are common in Canada, the US and Australia.
posted by MuffinMan at 3:16 AM on January 31, 2013


We have screens (monitors, ebooks, phones, etc.) on which we can rotate various 3D images of the planet, flip the map so Australia's on top, drag two country images around for a side-by-side comparison, recolor or resize everything according to arbitrary numbers such as population or wealth, and so on. We can all see different views based on our locations and preferences. We can project any of these electronic maps on to flat or curved surfaces and even print in 3D.

So, other than just for fun, how much do we really need to worry about whether our paper world maps are good enough?
posted by pracowity at 3:48 AM on January 31, 2013


So, other than just for fun, how much do we really need to worry about whether our paper world maps are good enough?

Because people are lazy? The Mercator projection is still everywhere even though we've had plenty of other projections for a long while. Travel site maps, Google maps, User location maps...these are all still using Mercator. People use this flat map on their flat screens even more now. So it is arguably even more important that people understand its limitations.
posted by vacapinta at 3:58 AM on January 31, 2013 [2 favorites]


So, other than just for fun, how much do we really need to worry about whether our paper world maps are good enough?

I think so. Look at Greenland. Would you realise it is actually the size of Saudi Arabia and less than a third of the size of Australia?

Yes, you can manipulate things, but only if you know what you're taking it from and to.
posted by MuffinMan at 4:16 AM on January 31, 2013 [1 favorite]


I KNEW THAT TWO OF THOSE BITS WERE THAILAND AND MONGOLIA BUT THEY JUST WEREN'T TURNING GREEN WHAT THE FUCK
posted by EmpressCallipygos at 4:17 AM on January 31, 2013 [9 favorites]


They're doing it again, playing with the world.

We have nothing to fear. They can't even locate themselves.

True - still, they're closer to discovery.

Patience. Look how long it took them to leave the atmosphere, drink potable water, walk upright. They notice themselves and no other.

So...we wait?

We wait. Oh look, one just found Mongolia! Yes, we wait.
posted by Lipstick Thespian at 4:33 AM on January 31, 2013 [2 favorites]


It's great. Even better would be if it offered random countries each time, in random locations. Then I'd waste days on it...
posted by rory at 4:39 AM on January 31, 2013 [3 favorites]


Cartographical Map Projections - everything you could want to know and more.
posted by the man of twists and turns at 5:26 AM on January 31, 2013 [3 favorites]


Okay, the point of the Mercator projection is simple. Navigation. On the Mercator projection, a rhumb line1 is a straight line. Rhumb lines are not great circles, but they're easy to hold course on -- you just set a bearing on the compass and hold it.

Which is why whole-world Mercator projections are so pointless - the scale makes them unsuitable for actual navigation, which is the whole point of Mercators.
posted by atrazine at 5:31 AM on January 31, 2013 [3 favorites]


vacapinta, YES! YES! Like those! Thankyouthankyouthankyou!
posted by Dysk at 5:51 AM on January 31, 2013 [1 favorite]


Greenland is still quite big, it seems, despite the Mercator bullshit.

Yeah, that surprised me too. It's still as big as the entire US East Coast.
posted by smackfu at 6:07 AM on January 31, 2013


This is a very cool way to prevent this information!

(I got South Africa right away because I'd just read an article at Strange Maps about the morphology of nations.)
posted by BrashTech at 6:09 AM on January 31, 2013 [1 favorite]


The Mercator projection is still everywhere even though we've had plenty of other projections for a long while. Travel site maps, Google maps, User location maps...these are all still using Mercator.

It's not because Google doesn't have the brains or money to implement other projections, so I'm sure they've decided that Mercator works best for their purposes -- it zooms without deforming, it's familiar and quickly understandable, etc. Something like 99.9999 percent of their users just want to know the fastest driving route from Des Moines to Dubuque (answer: take the Lincoln Highway to avoid Cedar Rapids). You can't expect Google Maps to switch projections just to reeducate the world about the actual size of Greenland in relation to Australia. (And there's always Google Earth for that.)

To fix education, you have to go to schools and make sure they put good geography apps on student screens. Make them drag countries around on the map the way we were just doing, etc.
posted by pracowity at 6:10 AM on January 31, 2013 [3 favorites]


Yeah, I hadn't had coffee yet. Sorry, ApathyGirl.

Moving on, I'm a huge fan of Desktop Earth, which uses images from NASA's Blue Marble Next Generation and cloud data from satellite photos to put a near-real-time view of the Earth and its atmosphere onto your desktop. Sadly, it's for Windows only.
posted by ob1quixote at 6:25 AM on January 31, 2013


So the rationale for the Mercator projection is ease of navigation. That's not difficult to accept as historical fact. However, to come to a firm intuitive notion of the value of this projection, look at a map of the moon. Notice how circular craters remain circular near the poles.
posted by rlk at 6:34 AM on January 31, 2013 [1 favorite]


To fix education, you have to go to schools and make sure they put good geography apps on student screens. Make them drag countries around on the map the way we were just doing, etc.

Actually one of DCPS's less egregious sixth grade Social Studies standards involved students being able to explain that you can't make an appropriate flat map of a three dimensional surface. We worked on this for a little while, comparing different maps and looking at their pros and cons. The problem a lot of my students saw with things like the Butterfly map mentioned above are that they're really difficult to use unless you already have a good sense of where things are relative to each other; you really have to think about (or even calculate) the distance between, say, Africa and South America and if you're a student with relatively poor map skills it just doesn't make any sense. There are uses for it, sure, but it's not at all intuitive and that's a big plus when looking at maps.
posted by Mrs. Pterodactyl at 6:35 AM on January 31, 2013 [1 favorite]


Also, I'm thinking it's time to get an enlarged world map to put above my desk. I'll also have to make sure to update it every couple of years, because I could not figure out what country Ukraine was for the life of me. Mainly because that shape wasn't a country the last time I carefully studied a world map.
posted by ob1quixote at 6:45 AM on January 31, 2013


I'm just angrily smashing Australia into Khazakstan over and over. WHY YOU NO FIT.
posted by elizardbits at 7:11 AM on January 31, 2013 [3 favorites]


these are all still using Mercator.

They're using the equirectangular projection which distorts the polar regions but doesn't gigantize them like Mercator.
posted by gubo at 7:29 AM on January 31, 2013 [1 favorite]


I was hoping it would give you different countries each time. Pity. Still, that was fun (once I stopped trying to shove Finland into east Asia).

I wish it would say what country it was when you added them. I had to look it up. Mauritania. Well, no wonder.
posted by It's Never Lurgi at 7:51 AM on January 31, 2013


I'm just angrily smashing Australia into Khazakstan over and over. WHY YOU NO FIT.

This summer, be amazed by elizardbits: The Old Testament.
posted by jaduncan at 8:19 AM on January 31, 2013 [1 favorite]


BrashTech: "This is a very cool way to prevent this information!

(I got South Africa right away because I'd just read an article at Strange Maps about the morphology of nations.)
"

Yeah, "perforated" countries are pretty rare so South Africa leapt out at me the same way. Once I realized that if the spot were a lake, it would not have been punched out...
posted by Karmakaze at 8:36 AM on January 31, 2013


Fun.
too bad the reset doesn't bring up a new set.
posted by OHenryPacey at 8:51 AM on January 31, 2013


I love this toy, it's a great demo. Projections are important, and while Mercator has its uses it's not a good choice for whole-world data visualizations. Mercator is a compromise, like all projections are. I think the main reason Google Maps uses it is because the resulting image is rectangular. Also at local scales the distortion is no big deal, at least if you're below about 60N. Interestingly Mercator is not always good for navigation; while straight lines are constant bearing, they are not great circles. That's why FAA publishes its aviation charts in Lambert Conformal Conic. Straight lines are (almost) great circles, although most pilots are reading the chart as if a straight line were also constant bearing.

If you're doing a visualization, take a look at the D3 Geo projection library. It comes with a whole variety of good projections and trying them all out is as simple as changing one line in your code. The basic Albers is good for US map data presentation. I've been using the Mollweide for some astronomy visualizations, but that's a weird case where you really care about the data all the way up to the poles.

Bonus link: Tissot's Indicatrix, a simple static visualization of the distortion of various projections. Basically it draws equal size circles all over the map; the amount they're distorted into ellipses is a quick view of the map distortion. More examples here. The Wikipedia articles on projections often render them, very helpful.
posted by Nelson at 9:01 AM on January 31, 2013 [3 favorites]


To be honest, the hardest part about that had nothing to do with Mercator projection - the hard part was things like trying to visualize Saudi Arabia without Yemen, Oman or the UAE tacked onto the south.
posted by Kid Charlemagne at 9:15 AM on January 31, 2013 [1 favorite]


Obligatory XKCD.


... I resemble that remark.
posted by the man of twists and turns at 9:18 AM on January 31, 2013


Every time one of these geography games comes up, I remember how embarrassingly ignorant I am about the geography of South America, Africa, and Southeast Asia. (Central Asia I'm pretty good with ever since my brother drove the Mongol Rally.) "Self," I say, "We have got to remedy that." And then I don't.
posted by KathrynT at 9:44 AM on January 31, 2013 [1 favorite]


Scratch my earlier comment, looks like Google Maps does do Mercator. I was thinking Google Earth overlays.
posted by gubo at 10:12 AM on January 31, 2013


Yes Ukraine was the last one. I blame the fact that it looks completely different in Risk.
posted by ckape at 10:22 AM on January 31, 2013 [2 favorites]


I'm embarrassed to admit how long I struggled to place a few of those before realizing I could zoom in just like in regular Google maps. Then it was much easier.
posted by caution live frogs at 11:44 AM on January 31, 2013


Also at local scales the distortion is no big deal, at least if you're below about 60N.

There is very little local distortion at virtually all latitudes. This is a consequence of the fact that angles on the map are correct bearings. That means that two streets that meet at a certain angle will always be represented that way on the map. This is very nice for road maps. Google maps is used for a lot of things but it's really engineered around street navigation.

The scale varies according to how far from the poles you are, so you'll only see distortion when when one part of your map is significantly closer to a pole than another. So a map of the Svalbard archipelago (74N - 81N) will be distorted, but a map of any 50 mile area of Svalbard will be basically just as accurate as a 50 mile area around Quito. Though, at the equator, you do have to zoom in more steps to get to any given map scale.

Other projections would either always give you inaccurate local geometry at varying latitudes, or have to stretch things out as you zoom in and out, both of which stink. I was never a big fan of the Mercator projection, but it looks like it really is the right choice for Google maps.

Drat.
posted by aubilenon at 12:03 PM on January 31, 2013 [1 favorite]


I can't believe it took me so long to get SA. You'd think Lesotho would be a dead giveaway. I kept thinking it was a lake.
posted by leotrotsky at 1:45 PM on January 31, 2013


Ha, there is Google Street View in the Svalbard archipelago. Fascinating.
posted by desjardins at 2:16 PM on January 31, 2013 [1 favorite]


35 years of being taught how inaccurate this map projection is, 10 years of working with maps professionally, and STILL today I said "Greenland is really that small?"
posted by kostia at 7:06 PM on January 31, 2013 [1 favorite]


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