It just depends on how much the computer can take, is my experience with this.
It's different for different computers.
For example: My computer can only go up to the map with a size of 100,000x100,000.
Anything after that makes it crash.
And I personally think 99,000 is a fairly large map. :3 You don't have to go up to extremely big sizes like 200,000 to make a good map.~