"Joatman71" (clip) Is there any way to make this proper curve without trial
and error? How is it best done using trial and error? (clip)
^^^^^^^^^^^^^^^^
Look in a map book. One of the ways of developing a global map is commonly
seen in geography books and atlases. Or, you could carefully peel an orange
to produce the shape you want. Or you could cover a ball with masking tape,
and then make the required cuts to produce the shape you need--then
carefully peel it.

Another idea is to take something like a croquet ball and hold it against a
belt sander until the outside is converted to the shape you are aiming for.