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Mercator Puzzle

gmaps-samples.googlecode.com

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Re: Mercator Puzzle

#71

Post by homosaur »

eru wrote: post #62
Millennium wrote: post #53

Earlier quoted context omitted.

The thing is, Mercator was never actually intended to be used as a map, per se. What it was supposed to be used for was a navigation chart, and it's extremely useful in that context: straight lines on the map correspond to straight lines in the real world, the compass directions are the same no matter where you look, and so on. Other projections distort these things, and there can be good reasons to do that depending…

Unless you want to find a straight line (great circle) between two distant points.

You would almost never strictly use a map for this purpose historically, you'd calculate it using tools.

Re: Mercator Puzzle

#72

Post by RobotCaleb »

jasondavies wrote: post #54
a3_nm wrote: post #30

Earlier quoted context omitted.

Not sure if this makes sense, but couldn't they have different projections for different zoom levels?

Yes, e.g. http://cartography.oregonstate.edu/demos/CompositeMapProject...

That's really cool. Thanks for sharing.

Re: Mercator Puzzle

#73

Post by [deleted] »

benjoffe wrote: post #31
a3_nm wrote: post #30

Earlier quoted context omitted.

Not sure if this makes sense, but couldn't they have different projections for different zoom levels?

As far as I can tell that actually could work very well, though the implementation might be quite difficult: 15 different zoom levels (I think) that google uses probably wouldn't be enough to make transitions between each seamless, requiring client side scaling during the zoom animations (which will either make the images slightly blurry or require loading higher resolution images).

[deleted]

Re: Mercator Puzzle

#74

Post by schiffern »

jasondavies wrote: post #25
jemfinch wrote: post #24

Earlier quoted context omitted.

I think this is an externally visible link: http://productforums.google.com/forum/#!topic/maps/A2ygEJ5eG... . It's the answer I received when I filed an internal bug on this. "Hi John - Thanks for the feedback. Maps uses Mercator because it preserves angles. The first launch of Maps actually did not use Mercator, and streets in high latitude places like Stockholm did not meet at right angles on the map the way they d…

Yes, there are two properties that are important for Google Maps: 1. Mercator is conformal, which means angles are preserved. So if you zoom into any small part of the map, it will look right. Equal-area maps distort angles. 2. North is always in the same direction—up. Together with the conformal property, it means that all directions are preserved: North, South, and everything else. The primary use case for Google M…

Of course, Google Maps isn't subject to the same limitations as paper maps – the projection could vary with both position and zoom level.

There are design and technical concerns, but they are not insurmountable. After all, if you ignore tilting then Google Earth is essentially a dynamically redrawn (position and scale variant!) planar map projection. With the proliferation of vector maps on mobile and WebGL in the browser, it seems like a solution could be found.

Re: Mercator Puzzle

#75

Post by stcredzero »

Got it. Zooming is essential on a tablet, because of the "my fat finger is in front of my eyes" problem, which I've solved, by the way. As it is, you have to zoom in to be able to see and drag.

(I took down the solution. If someone knows their way around VNC, it will get posted faster.)

Re: Mercator Puzzle

#76

Post by schiffern »

a3_nm wrote: post #30
jemfinch wrote: post #24

Earlier quoted context omitted.

I think this is an externally visible link: http://productforums.google.com/forum/#!topic/maps/A2ygEJ5eG... . It's the answer I received when I filed an internal bug on this. "Hi John - Thanks for the feedback. Maps uses Mercator because it preserves angles. The first launch of Maps actually did not use Mercator, and streets in high latitude places like Stockholm did not meet at right angles on the map the way they d…

Not sure if this makes sense, but couldn't they have different projections for different zoom levels?

Of course. The real challenge is making it look good with pinch-to-zoom.

Re: Mercator Puzzle

#77

Post by schiffern »

eru wrote: post #62
Millennium wrote: post #53

Earlier quoted context omitted.

The thing is, Mercator was never actually intended to be used as a map, per se. What it was supposed to be used for was a navigation chart, and it's extremely useful in that context: straight lines on the map correspond to straight lines in the real world, the compass directions are the same no matter where you look, and so on. Other projections distort these things, and there can be good reasons to do that depending…

Unless you want to find a straight line (great circle) between two distant points.

Great circles are not straight lines on the Mercator projection. Rhumb lines are straight, but not great circles.

If you want great circles to be straight lines, use the Gnomonic projection.

http://demonstrations.wolfram.com/GreatCirclesOnMercatorsCha...

http://en.wikipedia.org/wiki/Gnomonic_projection

Re: Mercator Puzzle

#78

Post by schiffern »

pc86 wrote: post #55
zokier wrote: post #21

Does anyone know why Google insists on Mercator projection? I guess that it makes the implementation bit simpler, but on the other hand you'd imagine that if anyone then Google would have the resources to use some more reasonable projection for greater good.

I understand that Mercator isn't the most accurate representation, but seriously, "greater good?" There are a lot of things that I think Google can do "for greater good," and changing how they show a map isn't even in the first hundred pages.

The bang for the buck is pretty good though.

Most people don't own an Atlas anymore. In the public consciousness Google Maps is the world map. If choice of map projection is important anywhere (which is debatable), it's important on Google Maps.

And remember: you can always fail over to Mercator.

Re: Mercator Puzzle

#79

Post by lmm »

SCAQTony wrote: post #13

That was boss, "only" took me a 30-minutes! Well done and great for learning geography.

Seriously 30 minutes? Is this an American thing? To my mind almost all of them were obvious from the shapes alone (the one with straight edges wasn't, but the very fact that its borders are straight lines tell you there's only a few parts of the world it could be in).

Re: Mercator Puzzle

#80

Post by finnw »

jasondavies wrote: post #25
jemfinch wrote: post #24

Earlier quoted context omitted.

I think this is an externally visible link: http://productforums.google.com/forum/#!topic/maps/A2ygEJ5eG... . It's the answer I received when I filed an internal bug on this. "Hi John - Thanks for the feedback. Maps uses Mercator because it preserves angles. The first launch of Maps actually did not use Mercator, and streets in high latitude places like Stockholm did not meet at right angles on the map the way they d…

Yes, there are two properties that are important for Google Maps: 1. Mercator is conformal, which means angles are preserved. So if you zoom into any small part of the map, it will look right. Equal-area maps distort angles. 2. North is always in the same direction—up. Together with the conformal property, it means that all directions are preserved: North, South, and everything else. The primary use case for Google M…

Interesting. From this description I would expect that mercator would always agree with lat/long in terms of "Is X North or South of Y" questions.

However, Albany (Australia) appears to be South of Melbourne when in its starting position on this map (inverted when moved to its correct position.) How is this possible?

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