----------------------------Original message---------------------------- A map dealer asks what does the "T" or "AT" stand for on elevations written in long-hand on 7.5' USGS provisional topo maps. I promised him I'd ask the list. Speaking of this series, has the USGS updated the explanation sheet describing topo map features recently? A single-sheet giveaway describing all the mundane map features and additionally some of the more technical aspects such as definitions of what all the tick marks along the edges mean would be very helpful for the common map user.