| Example 1: Military personnel position themselves for the Saber Arch ceremony. The soldiers are standing along two  lines parallel to a straight line coming down the center of the airplane staircase. They are also all standing the same distance from that center line. The soldiers are forming a locus of points. Set of points: the soldiers' locationsCondition: Saber Arch ceremony
 Locus: 2 lines parallel to the center line,
 and an equal distance from center line
   |  This 2007 photo shows Secretary of Defense Gates, his wife and former President Bush being welcomed in Texas. | 
                         
                         
                           | Example 2: Fifteen years ago, a series of trees were planted along a straight line driveway leading to an estate.  Each tree was planted the same distance from the center of the driveway. Set of points: the trees' locationsCondition: as a driveway border
 Locus: 2 lines parallel to the center line,
 and an equal distance from center line
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