It’s hard for me to believe that if the Empire and the First Order had a map of that region of space, but the Resistance didn’t. After the fall of the Empire, the Rebels would have had access to many imperial bases, ships, computers, records, etc.

Also, I don’t see how R2 could have had the map before Luke left because the map has a line showing which planets Luke has been to. I mean, maybe it’s a map that Luke found, and the line is showing the migrations of the ancient Jedi or whatever, but that’s never stated in the film. I also don’t see why he would leave that in R2 before he left if he was trying to prevent anyone from following him.

This seems like a pretty big plot point to me, since the entire plot of TFA revolves around one fragment of this map. I mean, who knows, maybe this is all explained in the next movie…but if it’s not, I think it’s a major plot hole.