Skip the map, the text is vastly more important and it refernces a map that is extant. The bottom line is that Columbus had a map to confirm the existence of serious landfall and he also knew of the wind direction in the northern latitudes. He really needed both. Key is that he knew he could come back.
It also appears fully authentic and has not been lost so it is a real treasure. I look forward to reading a translation.
It is also noteworthy that this brother had an excellent career as well after the discovery.