In thinking about this map, remember that obesity is a social construction and the Body Mass Index (upon which this map is based) is a controversial measure. See this really interesting flickr collection of people posing with their BMI scores.
I am curious as to your guesses as to what might cause this variation. I know that obesity is related to poverty (because healthy food is more expensive and more difficult to find than unhealthy food). Any other guesses?
Thanks to Breck C. for the link! Found here.