What makes a hill a mountain? In my definition in the gallery of erosional landforms, I cite a criterion of 300 meters, a thousand feet. In Britain, the Ordnance Survey defines a mountain at twice that height. Hillclimbing is such a popular pastime there that it makes a real difference if you can claim that your local peak is a bona fide mountain, even if it's just a few centimeters higher than the 600 m cutoff. Today on the GIS Lounge, Caitlin Dempsey reports on the efforts of a couple of guys who have been re-surveying the hilltops of Britain, using high-grade GPS equipment, to make sure that every mountain shall be exalted. Thack Moor, their latest certified triumph, is now England's 254th mountain.