The US is still of two minds on marijuana: While 16 states now consider it a medicine, others continue to hand down heavy sentences—including jail time—for simple possession. The result is a fractured market with prices that vary wildly by region. Not surprisingly, the actual numbers are hazy; there’s no price index for pot as there is for hops or tobacco. But a collective of geographers called Floatingsheep recently set out to clear the air. They gathered more than 14,700 consumer reports submitted anonymously on the site PriceOfWeed.com, stripped out the outliers, and created a map that inte...