My understanding is that it is a map based on Luke’s last known locations, and that data was split between what the Church of the Force knew and what the empire knew.
EFIT: So I thought that the crawl could be edited to remove references to a map and instead say that the old ally has data on Luke’s last known location. We could infer then that BB-8 isn’t carrying a map, but that data, which is only being called a map cus it’s easier?
Idk.