party  chief.  It  usually  consists  of  a  distance- measuring  crew,  an  angle  crew,  sometimes  a  level crew,  and  other  support  personnel.  This  break- down  of  personnel  is  ideal;  but,  on  many occasions,   the   same   personnel   will   have   to perform  a  variety  of  tasks  or  functions.  Therefore, each party member is trained to assume various duties and functions in several phases of the work survey. CONDUCTING   A   RECONNAISSANCE Whenever possible, a reconnaissance must be made to determine the starting point, the route to  be  followed,  the  points  to  be  controlled,  and the closing station. When selecting the starting and closing   points,   you   must   select   an   existing control station that was determined by a survey whose order of accuracy was equal to or greater than  the  traverse  to  be  run.  When  running  a traverse in which the direction of the traverse lines are not fixed before the start, select a route that offers  minimum  clearing  of  traverse  lines.  The best available maps and aerial photographs should be  used  during  the  office  and  field  reconnaissance. By selecting a route properly, you can lay out the traverse to pass relatively close to points that have to  be  located  or  staked  out. On  other  surveys,  such  as  road  center  line layout,  the  directions  of  the  traverse  lines  are predetermined,  and  all  obstructions,  including large trees, have to be cleared from the line. Often the assistance of the equipment and construction crews is needed at this point. For the lower order surveys  and  where  taping  is  used,  the  exact  route and  station  locations  normally  are  selected  as  the traverse  progresses.  These  stations  have  to  be selected so that at any one station, both the rear and   forward   stations   are   visible,   and   only   a minimum number of instrument setups is kept, reducing the possibility of instrument error and the  amount  of  computing  required. Furthermore,  the  electronic  distance-measuring devices  (EDMs)  have  made  traverse  reconnaissance even more important. The possibility y of using an EDM should be considered after the general align- ment in direction and the planned positioning of stations.  A  tower  or  platform  installed  to  clear surface  obstruction  will  permit  comparatively  long optical sights and distance measurements, hence avoiding  the  necessity  of  taping  it  in  short increments. PLACING  STATION  MARKS Some station marks are permanent markers, and  some  are  temporary  markers,  depending  upon the  purpose  of  the  traverse.  A  traverse  station that  will  be  reused  over  a  period  of  several years is usually marked in a permanent manner. Permanent traverse station markers are of various forms,   including   such   forms   as   an   iron   pipe filled  with  concrete;  a  crosscut  in  concrete  or  rock; or a hole drilled in concrete or rock and filled with lead,  with  a  tack  to  mark  the  exact  reference point.  Temporary  markers,  on  the  other  hand,  are used  on  traverse  stations  that  may  never  be reused, or perhaps will be reused only a few times within a period of 1 or 2 mo. Temporary traverse station markers are usually 2-in. by 2-in. wooden hubs,  12  in.  or  more  in  length.  They  are  driven flush with the ground and have a tack or small nail on top to mark the exact point of reference for angular and linear measurements. To assist in  recovering  the  hub,  a  1-in.  by  2-in.  wooden guard stake, 16 in. or more in length is driven at an angle so that its top is about 1 ft over the hub. Keel  (lumber  crayon)  or  a  large  marking  pen  is used to mark letters and/or numbers on the guard stake to identify the hub. The marked face of the guard stake is toward the hub. Since many of the hubs  marking  the  location  of  road  center  lines, landing  strips,  and  other  projects  will  require replacement  during  construction,  reference  marks are placed several hundred feet or meters away from  the  station  they  reference.  Reference  marks, usually  similar  in  construction  to  that  of  the station  hub,  are  used  to  reestablish  a  station  if its  marker  has  been  disturbed  or  destroyed. NOTE:  Procedures  for  marking  hub  and guard stakes for traverse stations, road center line layout, and other surveys are presented in the next chapter. TYING  IN  TO  EXISTING  CONTROL As  we  discussed  earlier  in  this  chapter,  the starting  point  of  a  closed  traverse  must  be  a known position or control point; and, for a closed loop traverse, this point is both the starting and closing  point.  Closed  connecting  traverses  start at one control point and tie into another control point. A traverse starting point should be an existing station with another station visible for orienting the new traverse. The adjacent station must be intervisible with the starting point to make the tie 13-28