For my own fun and possible use I'm fiddling around with an idea for a tabletop RPG setting. One of the core concepts of this setting is that the world is so large that no one has ever even heard rumors of there having been seen an end to it. I do actually plan to make an actual round planet. I imagine it would need to be at least ten times as large as the earth if not larger but I was hoping those that find the idea interesting might be willing to join a discussion about it with me here. Help me do a better job of it.

So far I thought I'd get some opinions and maybe look around a little bit so I can decide on a proper general size. Then maybe look just a little into enough of how to do things properly so that geography fans wouldn't cringe at the sight of it. Get the general size of continents, large bodies of water, and mountains for the entire planet. Then select a large reason to be the default activity area for the setting. Fill in more details for that area. Rivers, lakes, forests, plains, and that sort of thing.

I'm hoping to learn if I'm on entirely the wrong track there. Are there more efficient ways to go about this? Hangups to avoid? Useful software? Any constructive input would be welcome.

A little basic idea on the RPG setting for those interested in leaving comment. It's a medium to high fantasy setting that I am building for the GURPS system. Technologically it will be advanced to the point of muskets and such but I plan to have technology pretty much permanently stunted in most areas. Civilization will be confined to very large, walled city states surrounded by wilderness that simply will not be tamed. So likely travel distances in a life time will be limited. Even for large flying creatures territory of other powerful creatures and such would likely have an effect.

So, any thoughts or comments?