I think the rules make this point pretty clear. I don't have my Rio Grande Rules here but the translation on the geek says the following:
rules translation wrote:
Note: although the zones and areas are similar, they are not exactly the same. Specifically, the yellow nautical station for zone I is in the second area (blue) as are all the nautical stations for zone II. All of the nautical stations for zone III lie in the third area (red).
Warning: total assumption on my part below
Spoiler (click to reveal)
I assume that "areas" and "nautical zones" were originally intended to be the same but in play testing it was found that the yellow station was too easy to get to so they moved it into the 2nd "area" (or some such)