I’m confused about Luke’s map as well. At first I thought it has been specifically designed by him so that only Rey could find him, but it makes sense only if he had somehow forseen her future, which would possibly lead to more inconsistencies.
The only people talking to each other remotely in the OT were Luke, Leia (in TESB, when she was not Luke’s sister yet), and Vader. It may be it only works at close range, as Vader still has to get into the Emperor’s room to talk to him.

P.S.: Abrams talks about the map here http://www.ew.com/article/2015/12/20/jj-abrams-answers-burning-question-about-r2-d2-star-wars-force-awakens
From what I understand, more than a map leading to Luke, they were going for a map leading to a specific location, possibly known by name but unmarked on any map (kind of like in AOTC).