From: rshepard@salmo.appl-ecosys.com   
      
   On 2004-08-17, Robert Oliver  wrote:   
      
   > Situation:  An air traffic control display depicts aircraft using position   
   > symbols and labels.  Position symbols show the two dimensional location of   
   > each aircraft.  Labels contain additional aircraft data and are (usually)   
   > connected to its associated position symbol by a line.  Labels which overlap   
   > are obscured.   
      
   Bob,   
      
     Allow me to take a different approach than that offered by Bill. My   
   thoughts are based on these assumptions:   
      
     - Labels can overlap but symbols cannot.   
     - The overlap time is minimal.   
     - There is a non-random algorithm that determines label position relative   
   	to its parent symbol.   
     - Controllers build mental maps of existing patterns quickly.   
     - Changes to those patterns draw attention to potential airspace   
   	conflicts.   
      
     If these are valid, then moving labels (some slow, some fast) may be   
   disruptive to maintaining a mental image of the entire pattern and movements   
   of the positional symbols. The labels are informational, certainly, but   
   secondary to the spatial distribution and movement of symbols. I would   
   consider enlarging the label that is about to be overrun by another one for   
   the duration of the overlap. Even if the rear one is obscured, its presence   
   is denoted by a larger label behind the visible, near one. The controller   
   can bring up the information on the hidden label by moving the cursor (light   
   pen, whatever) to the pair and initiating an event. The two labels then   
   reverse their positions in the stack.   
      
     I think that the most pragmatic solution depends on the number and   
   duration of label overlaps. I imagine that at O'Hare the display is a solid   
   mass of moving symbols and labels and not much would help. However, on the   
   up side, moving labels would not add much more activity to the display but   
   would keep all labels visible at all times. This would not be the problem   
   at, for example, the Pocatello, Elko or Bozeman airports.   
      
   Rich   
      
   --   
   Dr. Richard B. Shepard, President   
   Applied Ecosystem Services, Inc. (TM)   
      
      
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