(Edit - I misread my own math here) Not sure where 21% comes from - if 3/10 of points are on land, 9/100 antipode-pairs should be land-land, and that means 9/1

(Edit - I misread my own math here) Not sure where 21% comes from - if 3/10 of points are on land, 9/100 antipode-pairs should be land-land, and that means 9/100 / 30/100 = 9/30 = 30% of land should have land opposite it, and conversely 70% should have water? But the true numbers are 15%/85% - on the actual earth, land is more likely to have ocean opposite it than random chance would suggest. Analyzing whether items sufficiently far from the ‘expected’ random distribution as to be statistically significant is a rather different exercise though.