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by Retric 4065 days ago
Gall-Peters is also a conformation projection that maps north-south maps to the vertical axis, and east-west to the horizontal axis. As to online maps one major advantage is the X-Y scale does not get nearly as messed up at multiple zoom levels.

However, online maps alter the projection as you zoom so this is not much of an issue.
1 comments
mewo2 4065 days ago
Gall-Peters is definitely not conformal. It preserves area, but greatly distorts angles, apart from at the two standard parallels of 45 degrees north and south. This results in the shapes of land masses getting very squished towards the poles (and to a lesser extent, the equator). For an example, look at the shape of Greenland, which appears twice as wide (east-west) as it is tall (north-south), when in reality it's the other way around.

I'm also not aware of any of the main online maps changing projection as you zoom. It seems like that would be more pain than it's worth.

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Retric 4065 days ago
A Mercator projection (ed: is a Conformal map, but) it also greatly distorts both angles and shapes as you approach the poles. The trivial example is to walk a square mile (N,W,S,E) you would expect the opposite sides to be at 45deg angle, but on Mercator the sides get stretched so a square in the real world can have a 10+:1 or even 100:1 side lengths on a Mercator map.

The property they both preserve is points north, south, east, or west of them on a globe are also north, south, east, or west of them in the projection. (Plenty of rectangular projections don't have this property ex: http://geographer-at-large.blogspot.com/2011/08/fun-with-map...)

The issue is interior angels of a triangle on a sphere don't add up to 180 degrees so you literally can't preserve all angles on a projection.

PS: If you actually walk exactly 1 mile north, 1 mile west, 1 mile south, then 1 mile east you don't necessarily end up on exactly the same place on a globe. (It does work if you start half a mile below the equator.)

Edit: Not that the earth is even a sphere...

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vilhelm_s 4065 days ago
It preserves angles locally. https://en.wikipedia.org/wiki/Conformal_map
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Retric 4065 days ago
Yea, nm I was wrong. Shapes do get distorted near the poles, but at fixed latitude the distortion decreases as their size decreases.
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