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There is some convention? how is this 3d to 2d mapping done?

here an example

Fermi_Data

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The ellipse is a particular way to draw the surface of a sphere - like the sphere of the skies around us, or the surface of the Earth - on a flat piece of paper or screen (because of the curvature of the sphere, it cannot be "flattened" without distortions). This one is called the Mollweide projection and it preserves the areas (and completely sacrifices correct representation of the angles):

http://en.wikipedia.org/wiki/Mollweide_projection
http://en.wikipedia.org/wiki/Map_projection

The second link enumerates many other ways how to draw the spherical surface.

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  • $\begingroup$ This is effectiveness! (but you lose the secret ballot haha) i.imgur.com/WhUQQ.jpg $\endgroup$ – HDE Mar 3 '11 at 13:28
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    $\begingroup$ Haha, one vote, one answer, one view, one God. ;-) I don't want to translate it into German because it would sound like Eine Volke etc. I actually wrote the answer when the question had minus five views, but waited for 6 more people to view it in order to make everyone believe that I am constrained by causality, too. $\endgroup$ – Luboš Motl Mar 3 '11 at 18:00

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