So I found out their explanation for R2D2 having the map and suddenly turning on 
: "But Abrams and screenwriter Michael Arndt did move to fill in one plot hole which fans have complained about in The Force Awakens, R2-D2’s ability to “fill in” the map to Skywalker near the movie’s denouement. The idea, Arndt revealed at a post-screening Q&A, picked up on a scene in 1977’s Star Wars in which the astromech droid is able to scan the Empire’s mainframe while the heroes hunt for Princess Leia on a star ship.
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“We had the idea about R2 plugging into the information base of the Death Star, and that’s how he was able to get the full map and find where the Jedi temples are,” said Arndt. Added Abrams: “BB-8 comes up and says something to him, which is basically, ‘I’ve got this piece of a map, do you happen to have the rest?’ The idea was, R2 who has been all over the galaxy, is still in his coma, but he hears this. And it triggers something that would ultimately wake him up.”
Continued Abrams: “While it may seem, you know, completely lucky and an easy way out, at that point in the movie, when you’ve lost a person, desperately, and somebody you hopefully care about is unconscious, you want someone to return.”
http://www.theguardian.com/film/2015/dec/21/jj-abrams-reveals-ewan-mcgregor-obi-wan-kenobi-in-star-wars-the-force-awakens
