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          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.