The idea is to draw a red line over every completed trail in the Appalachian Mountain Club’s “Guide to the Paths and Camps in the White Mountains,” which was published in 1907. It’s called redlining—and it has become increasingly popular, according to The Boston Globe. (The story even profiles a “gridder,” someone who climbs all forty-eight 4,000-foot peaks 12 times each, once in each month of the year