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I don't know what you mean about the aspect ratio further from the equator. Mercator is conformal, it preserves angles, so the aspect ratio is 1:1 everywhere th

by rspeer 9y ago

I don't know what you mean about the aspect ratio further from the equator. Mercator is conformal, it preserves angles, so the aspect ratio is 1:1 everywhere that it makes sense to say "aspect ratio". Are you talking about the problem with the shape of a Mercator tile becoming absurd very close to the poles, which I wouldn't call "aspect"? Or are you thinking of the equirectangular projection, where the aspect ratio changes to preserve the distance between latitude lines? The reason not to use a globe is efficiency. Not only is 2D easier than 3D, but you can make Mercator out of tesselated tiles. You can't do that on a globe without having way too many tiles or obvious seams.

robbrown451 9y ago
Right but things like google maps doesn't really use tiles anymore as far as I can tell, they do it using vectors. Tiles suck for lots of things, for instance scrolling can move the street name off the visible map, while doing it as vectors the name can be adjusted.
- rspeer 9y ago
  The tiles aren't static raster images, but they're still tiles, made of vector data. You can see them while it's loading. This allows Google to cache the files they serve. And when you pan a Google Map, you're panning a flat Web Mercator projection. If it were a projection of the globe, then everything that's already been rendered would have to be adjusted by imperceptible subpixels to account for the curvature of the Earth.
  - robbrown451 9y ago
    Well if it vector data, the "tiles" can simply be a region of a sphere. That alone is not a reason for Mercator. There may be efficiencies of panning a flat projection, but that is becoming a smaller and smaller issue as devices get more capable. Also, even when in "map mode", you will often notice that google maps is doing more than that. Go to a place where there are tall buildings (I'm looking at downtown san francisco) and you can see the perspective shift on the buildings as it pans.

by rspeer 9y ago

robbrown451 9y ago

Right but things like google maps doesn't really use tiles anymore as far as I can tell, they do it using vectors. Tiles suck for lots of things, for instance scrolling can move the street name off the visible map, while doing it as vectors the name can be adjusted.

rspeer 9y ago
The tiles aren't static raster images, but they're still tiles, made of vector data. You can see them while it's loading. This allows Google to cache the files they serve. And when you pan a Google Map, you're panning a flat Web Mercator projection. If it were a projection of the globe, then everything that's already been rendered would have to be adjusted by imperceptible subpixels to account for the curvature of the Earth.
- robbrown451 9y ago
  Well if it vector data, the "tiles" can simply be a region of a sphere. That alone is not a reason for Mercator. There may be efficiencies of panning a flat projection, but that is becoming a smaller and smaller issue as devices get more capable. Also, even when in "map mode", you will often notice that google maps is doing more than that. Go to a place where there are tall buildings (I'm looking at downtown san francisco) and you can see the perspective shift on the buildings as it pans.