Although I know you are trying to do this to scale....maybe you should consider the maps of old as a partial guideline as well.Most cartographers though trying to do so would highlight the destination a little bit larger than scale...they were trying to define largely unknown properties and distances and they also wanted to inspire travel and marketing potential..the true figures were mostly in the ocean areas of the charts. this would give you a little leeway and let you play with the island a bit. Don't forget there were always sea monsters to beware of as well.....just a thought.