Small bug here, the map currently shows 100% explored but my quest is at 99%. I am assuming this is due to rounding up as I have only 3 squares left to uncover.
Could this be the same problem with my 75% exploration achievement? I hit 75% on the map, but the achievement hasn't hit, and I've even explored 3 more spaces since I got 75% and still nothing.
There are 600 squares, which implies each 1% = 6 squares, but are you sure it doesn't round that up? I could've sworn I got the 75% quest with 4 squares. I had 74%, completed one square, the bar went to 75%. pretty sure I got three more, and finished the quest. Take that with a grain of buckshot, tho. When It comes to numbers, I'm usually wrong.
I haven't seen an instance where it took less than 6 squares but maybe it's weighted in some way...after all, there are squares that automatically are uncovered and the squares that are initially uncovered...