trapper/kcmo
i could easily make a case that this is the period of the transformation from a minimum of iodine in our diet to no iodine and plenty of fluorides and bromides to take its place. i believe it is a really good picture of the growth of halide imbalance.
if you could go back, you would find people pigging out after WW2 and getting fat in the fifties. then, in 1959, things changed as iodine was introduced into the diet in sufficient amounts to protect against I-131, a toxic residue of the nuclear testing going on. this continued full force until 69 with a complete cessation in 1980 and bromides and fluorides were increased in usage.
in the sixties the obesity problem went away, the average 18yo high school senior girl was, on the average, 1 inch taller and 25 pounds lighter, test scores have never been higher, more people per capita graduated high school, went to college, and graduated college than ever before or since. cancer rates dropped.
so the maps should start about 1950 and we would see a much clearer picture. this was also the period that americans went from farm dwellers to city dwellers. a lot has changed and none of it is good. we are now the animals and this is the farm.