CLOSING  THE  HORIZON—Measuring  the  last of   a   series   of   horizontal   angles   at   a   station required to make the series complete around the horizon. At any station, the sum of the horizontal angles between adjacent lines should equal 360°. The  amount  by  which  the  sum  of  the  measured angles fails to equal 360° is the angular error of closure. This error is distributed as a correction among  the  measured  angles  to  make  their  sum exactly  360°.  The  error  and  the  correction  have opposite  algebraic  signs. COLLIMATE—Adjust  the  line  of  sight  of  a telescopic   surveying   instrument   to   its   proper position  relative  to  the  other  parts  of  the instrument. COLLIMATION   LINE—The   line   through   the second nodal point of the objective (object glass) of a telescope and the center of the reticle. It is variously  termed  the  line  of  sight,  sight  line, pointing line, and the aiming line of the instru- ment.  The  center  of  the  reticle  of  the  telescope of a transit can be defined by the intersection of cross  hairs  or  by  the  middle  point  of  a  fixed vertical wire or of a micrometer wire in its mean position.  In  a  leveling  instrument,  the  center  of the  reticle  may  be  the  middle  point  of  a  fixed horizontal  wire. COMMON   LOGARITHMS—Logarithms   with 10 as a base. COMPASS-PIVOT   JOINT,   BOW,   DROP BOW,  BEAM—Instrument  used  to  draw  circles or  arcs  of  circles. COMPOUND  CURVE—A  curve  composed  of  a series  of  successive  tangent  circular  arcs. CONE—A  solid  figure  that  tapers  uniformly  from a  circular  base  to  a  point. CONNECTING   TRAVERSE-A   closed   traverse that starts and ends at different stations whose relative positions have been determined by other surveys. CONSTRUCTION  LINES—Lightly  drawn  lines used  in  the  preliminary  layout  of  a  drawing. CONTOUR—An  imaginary  level  line  (constant elevation)  on  the  ground  surface;  it  is  called  a CONTOUR  LINE  on  a  corresponding  map. CONTOUR   INTERVAL—A   predetermined difference  in  elevation  (vertical  distance)  at  which contour lines are drawn. The contour interval is usually  the  same  for  maps  of  the  same  scale. CONTOUR   LINE—An   imaginary   line   on   the ground,   all   points   of   which   are   at   the   same elevation  above  or  below  a  specified  datum. CONTOUR MAP—A map that portrays relief by means  of  contour  lines. CONTROL—A  system  of  points  whose  relative positions   have   been   determined   from   survey data.   (See   BASIC   CONTROL,   HORIZONTAL CONTROL,   and   VERTICAL   CONTROL.) CONTROL   STATION—A   station   whose   posi- tion (horizontal or vertical) has been determined from  survey  data  and  is  used  as  a  base  for  a dependent survey. CONTROL   SURVEY—A   survey   that   provides positions   (horizontal   or   vertical)   of   points   to which  supplementary  surveys  are  adjusted. COORDINATES—Linear  or  angular  quantities, or both, that designate the position of a point in relation  to  a  given  reference  frame.  There  are  two general  divisions  of  coordinates  used  in  surveying: polar  coordinates  and  rectangular  coordinates. These  may  be  subdivided  into  three  classes:  plane coordinates,   spherical   coordinates,   and   space coordinates. COUNTERCLOCKWISE   ANGLE—A   hori- zontal   angle   measured   in   a   counterclockwise direction.  The  counterclockwise  angle  is  used primarily  for  the  measurement  of  deflection angles. COURSE—The direction of a line with reference to  a  meridian,  usually  given  as  a  true  or  as  a magnetic  bearing. CRUSHED  GRAVEL-The  product  resulting from   the   artificial   crushing   of   gravel   with substantially all fragments having at least one face resulting  from  fracture. CRUSHED STONE—The product resulting from the artificial crushing of rocks, boulders, or large cobblestones,  substantially  all  faces  of  which  have resulted  from  the  crushing  operation. AI-4