Round world border?

How do I get a round of Worldborder like in this picture in Minecraft 1.12.2?

And how do I manage to have such an expanded map as in this picture

Extended map = world type infinite if that is a limit, and not any appearances from the monitor. If you mean the visibility, you can turn it up in the graphics settings.
I don't know what a round world border should be.
But I can recommend the Realistic Terrain Generator for 1.12. Makes the whole thing more handsome.