Clarification on the Royal Garden from Puerto Rico expansion 2
In my opinion, a player's island is their game board, unless explicitly referring to plantations.  Its semantically tricky, as the island on the board contains San Juan which is implicitly the player's city.

I admit, that's kind of shaky reasoning.

With regards to the Royal Garden explicitly, an unofficial translation of the original rules was:


  At game’s end the owner of the Garden
  gains 2 VP for each Noble he owns
  instead of the usual 1VP/Noble. This
  is true wherever his Nobles are:
  building, plantation, San Juan, etc...


(source)

And it makes more sense in terms of design as the rest of the expansion clearly wants you to place Nobles on buildings.