Quote Originally Posted by heffnerc1 View Post
Fact: Spherical worlds presented on 2-D maps should generally be twice as wide as high, e.g., a 30" poster should be 15" high.
No, this is wrong.

There are a number of projections which map the surface of a sphere onto a shape with a 2:1 aspect ratio, but none of them is generally used for general reference maps like the typical wall map.

Tangent Equidistant Cylindrical gives a 2:1 rectangle, and is very simple, but also very ugly and it distorts both shape and area dramatically. It has some specialized uses but is not appropriate for a reference maps, particularly those involving density.

Mollweide and Hammer both map onto 2:1 ellipses, and both preserve areas. But as shape is generally more significant for reference maps, they aren't used much for wall maps. They are very good for thematic maps particularly those involving density.

Sinusoidal Is an equal area psuedocylindrical projection much like Mollweide, but the shape it forms is different, the area between two mirrored "humps" from a sine wave. It is 2:1, but its not often used for reference maps for the same reasons as Mollweide.

A pair of azimuthal projections of opposite hemispheres side by side has a 2:1 ratio (its two circles) and they have been used for reference maps, but they usually have additional components such as polar insets, titles, and other bits that reduce the aspect ratio significantly.

That doesn't mean you can just do whatever you want and have it work out, regardless of what aspect ratio or shape you use. If you want your world to really work (say you want to be able to display it on a sphere in 3D, or you want to be able to figure out proper spherical distance) you need to understand at least the rudiments of projections and spherical geometry. If you don't care about that and are happy with a world that is effectively flat or cylindrical (Or if it really is flat or cylindrical) then just do whatever looks good.