I've seen somewhere on the Internet the expression population shown as percentage of top nation and I simply can't see what is mean by that.
I can make a few guesses but none of them seem to be confirmed by the map's contents.
The values measured for each nation are shown as a proportion of the largest value measured. Israel has the largest Jewish population, so it gets a green dot representing 100%. France has about 10% as many Jews as Israel—about half a million—so it gets a yellow dot representing 10%. Russia has about 4% as many Jews as Israel, so it gets four red dots each representing 1%