The text mentions inches, but the map is apparently using centimeters (2.54 equals 1 inch). I think this is length, rather than circumference. And erect, I presume.
Ask our local pecker checkers! They should have an idea if race, IQ, height, or anything else makes a difference.
Of course there are outliers, like a 4 foot tall Chinaman with a 180 IQ and a 10 inch penis, but the girls should be able to give us an idea.
Keep in mind that any difference probably has to do with the amount of food available and the weather. Africa is hot. Africa hot. That means that a guy's junk is going to be on display and a bigger limp unit gets rid of more heat.
In Asia, people typically have less body mass due to their diets. An Asian gentleman needs to have a tool to fit petite Asian women. Anything more is biologically 'expensive' and pointless. Speaking of expensive...correlate body mass to brain mass. The brain needs lots of energy.