Same goes with Isle Delphino, it's somewhere out, over the oceans.
The Yoshis live on Yoshi's Island, which is the first world in SMW (so the most of SMW2 takes place their, except for the last world). But, in SMRPG, the Yoshis live on Yo'ster's Isle. What I think is that a different tribe (clan, pack, group, community, etc.) live on each island. But, then again, THE Yoshi lives on both islands.
They need to make a real map, it would be so cool. :-)