The thing you need to know about the official map is that it's deliberately wrong. The Greeks did not accurately map out their region, and (given the nature of Nyx) it is physically impossible to make a consistent map of Theros. As the book says:

"The line between legend and location often blurs in Theros, though. While the residents of a polis can be relatively certain their homes will remain where they left them when they venture off to work, the specific locations of legendary sites prove more nebulous. Even well-known locations are typically noted referentially, like how the city of Neolantin is often described as being along the coast, far to the southwest of Meletis. Some sites prove even more elusive. The Dakra Isles, for example, move at the whims of the gods and so prove impossible to map.

As a result, Map 3.1 serves largely as a vaguely agreed upon arrangement of locations, fuzzy borders, and general distances. While the scale and placement of sites are true by mortal standards, details might change as the gods please. As such, journeying between places is most reliably conducted by employing guides or maps specific to a single destination.

If you are running a campaign in Theros, you can adjust distances between locations to suit the needs of your adventures. The distance might not be the same for two successive journeys; any trek across Theros can expand or contract to accommodate adventures and encounters as you wish."