
Continuity mistake: After Leia tells Han that she always hated watching him leave and he still drives her crazy, they hug and it cuts to the Starkiller Base. When we see Stormtroopers walking through the corridor and then Rey sneaking away, it's a flipped shot - note the Stormtroopers' backs, and Rey's hip bag and leather wrist cuff. (01:35:15)
Answer: The First Order already has the piece that R2-D2 was carrying as well. That is the first piece, the large piece of the map missing a small section. The second piece is carried by BB-8 and only by BB-8, the missing piece in the map. All the first order needs is that second piece, and so does the Resistance. However the Resistance needs R2-D2 to activate again so he can show them the first piece, so they can put the second piece in it.
lionhead