What we know about it is that it's not Herodotos' map. He never made a map. In fact, no Ancient Greek maps survive to the present day (though we know they existed once).

The map that's going around the internet as "Herodotos' map" is an 18th-19th century work incorporating all the geographical information given by Herodotos. It's just a modern tool for readers of Herodotos who are more used to seeing this kind of information in map form, rather than in the form of the lengthy descriptions that Herodotos actually offers. You can make it yourself by reading Herodotos and keeping a blank piece of paper handy. It is in no way ancient, and it's not certain that Herodotos would have understood or approved of the map if it had been shown to him by a time traveller.

The map probably reflects the geographical knowledge available to an avid Greek traveller and researcher like Herodotos in the second half of the 5th century BC. That is to say, it accurately represents the regions surrounding the Eastern Mediterranean and the Black Sea, as well as the territory of urbanised societies like Mesopotamia and Egypt, but it gets increasingly fuzzy and based on hearsay as you move further away from those cores. On the fringes of the "known" world we find mythical peoples like the Androphagoi (people-eaters) and Macrobians (those who live long). The only feature in the far West that Herodotos was certain about was the Atlas Mountains, and so he called the people he figured would live over there "Atlantes" (people of Atlas).

In other words, the map is "valid" if you're looking to find out what a Greek of the Classical period might have known. It is not "valid" in the sense that it doesn't represent some form of lost or hidden geographical knowledge. All the parts of the map that don't correspond to modern maps are simply wrong; the Greeks didn't have the detailed knowledge or the mathematics to map them accurately.