In the interest of giving credit where credit is due, my avatar is a scan of a hand-drawn caricature by cartoonist Jim Naylor which was done at my company's 20th anniversary dinner.
I believe there is a slight discrepancy in the rules where it refers to only building on intersections of hexes.
The earlier editions did not come with the jigsaw-style frame - instead they came with additional sea-hexes (some of which had harbour markings) which were used to encircle the island. Thus all corners of all island hexes qualify as "intersections", even though with the frame they are not obviously intersections.
The fact that the rule book wording has not caught up with the redesign is clear when you consider that it defines an "intersection" as where 3 hexes meet, and yet both the beginners map and maritime trade example illustrations show settlements where only two physical hexes now meet.