covered If controlled photographs are available, the survey engineer can locate points by pricking or keying them  to  the  photographs.  An  uncontrolled  photograph may  be  satisfactory  for  the  surveys  of  low-order accuracy   mentioned   in   the   preceding   paragraph. According to the soils analyst’s instructions, the survey party chief prepares maps or overlays upon which he plots  the  control  and  ties  them  to  the  pedological features.  The  pedological  interpretation  of  aerial photographs is the responsibility of the terrain analysts. Plane Table Traverse The plane table traverse is best adapted to relatively open country for the preparation of the basic sketch upon which the soils engineer plots pertinent data. In the absence  of  detailed  instructions  from  the  soils  engineer, the  following  procedures  are  generally  satisfactory  for preparing a sketch of an area of several square miles (3 miles by 3 miles maximum for initial exploration): 1. SCALE: 1:12,500 or 1:25,000. 2.  TRAVERSE  CONTROL.  Run  in  circuits  or between known positions of a higher order of accuracy. 3.  SIGHTING.  Use  a  peep  sight  or  telescopic alidade. 4.  DISTANCE  MEASUREMENTS.  Pace  or obtain  a  rough  measurement  with  tape.  When  a telescopic alidade is available, use stadia measurements where possible (to reduce the time required for the survey, rather than to increase the accuracy). 5.   BASE   DIRECTION.   To   determine   a   base direction,  select  known  bases:  railroad  or  highway tangents, recognizable features, or reliable topographic maps.  In  the  absence  of  these  known  bases,  use magnetic  north  as  determined  by  compass  observations. 6.  COMPASS.  Use  military  compass,  forestry compass,  or  pocket  transit. 7.  DISTANCE  BETWEEN  BASIC  CONTROL POINTS. Maintain 3 miles as the extreme maximum distance  between  stations. 8.  ACCURACY.  Distances  should  be  measured  in such a manner that points can be plotted within 25 feet. For the scales suggested, measurements to 1 part in 100 will  suffice.  Take  sights  with  peep-sight  alidade carefully  to  maintain  directions  of  an  accuracy comparable  to  distances. 9.  TOPOGRAPHY.  Topography  is  usually  not required  on  reconnaissance  surveys  for  pedology, particularly  in  areas  of  low  relief.  Where  suitable deposits of sand, gravel, or stone have been located route surveys from the site to the point of use may be required for the location of haulage roads, conveyors, or other  means  of  transporting  the  material.  In  hilly  terrain, a  rough  topographic  map,  obtained  by  clinometer, pocket transit, or stadia, may be required to make the location of a favorable route easier. Compass  Traverse In heavily wooded areas, compass traversing is more convenient than plane table traversing; however, more  time  is  required  for  plotting  by  the  compass traverse method. Traverse lines between stations should be long to reduce the number of observed bearings. Points between stations are located by offsets from the traverse  lines.  Where  local  attraction  affects  compass readings, points are plotted by intersection. Survey readings  may  be  plotted  in  the  field.  Notes  should  be kept in case the traverse must be retraced. In the absence of detailed instructions from the soils engineer, the basic guides for plane table traverse apply. Field Sheets and Site Plans The survey engineer must furnish the soils analyst with  suitable  maps,  overlays,  and  sketches  for  the plotting of pedological data. After the preparation of a reconnaissance field sheet of an area of several square miles,  the  soils  analyst  may  require  a  sketch  of  a particular site in which many samples are taken for a more  detailed  study.  In  the  absence  of  detailed instructions, the surveyor prepares a sketch on a scale of 1 inch = 400 feet and provides ranges and reference points to aid in plotting or tieing in specific positions of auger holes, drill holes, and lines of exposed rock or other pedological features. For plotting the data of a range, cross section, or series of boreholes, the soils analyst may require the surveyor to provide a basic plot on a scale of 1 inch = 100 feet or of 1 inch = 200 feet. Survey measurements will be conducted accordingly. SOIL SURVEYS The survey of soil conditions at the site of proposed military  construction  provides  information  about  the nature,  extent,  and  condition  of  soil  layers;  the  position of the water table; drainage characteristics; and sources of possible construction materials. The survey of soil conditions is vital to both the planning and execution of military  construction  operations. 16-4