General 3D: Help on image to be wrapped around sphere for planet effect


I Have Maya 8 and Swift 3D V3, but this question is pretty much universal to all 3D apps.
(as well as Photoshop CS and CS2)

I will have to render a 3D sphere, with an image applied to it to show continents etc… of a fictional world.

I can apply images to spheres in both applications, thats not the problem.
I need help creating the image that will be used as a texture.

The planet may be fictional, but it has to be displayed and rendered correctly and accurately nonetheless. Its not a task that simply calls for “a planet” in the background. The planet is the focus, and has a name.

My largest problem is the image dimensions. What would the width and hight ratio be? If I get it wrong I could see things like the ice-caps being displayed wrong. I’m not overly concerned about drawing techniques to make the continents etc… realistic. Just the dimensions.

I’d appreciate any help, or suggestions.