TOPOGRAPHIC  SURVEYS The  purpose  of  a  TOPOGRAPHIC  SURVEY is  to  gather  survey  data  about  the  natural  and man-made  features  of  the  land,  as  well  as  its elevations.  From  this  information  a  three- dimensional  map  may  be  prepared.  You  may prepare  the  topographic  map  in  the  office  after collecting the field data or prepare it right away in  the  field  by  plane  table.  The  work  usually consists  of  the  following: 1.  Establishing  horizontal  and  vertical  control that  will  serve  as  the  framework  of  the  survey 2.   Determining   enough   horizontal   location and  elevation  (usually  called  side  shots)  of  ground points to provide enough data for plotting when the map is prepared 3.  Locating  natural  and  man-made  features that may be required by the purpose of the survey 4.   Computing   distances,   angles,   and elevations 5.  Drawing  the  topographic  map Topographic surveys are commonly identified with  horizontal  and/or  vertical  control  of  third- and  lower-order  accuracies. ROUTE SURVEYS The  term  route  survey   refers  to  surveys necessary  for  the  location  and  construction  of lines  of  transportation  or  communication  that continue  across  country  for  some  distance,  such as   highways,   railroads,   open-conduit   systems, pipelines,  and  power  lines.  Generally,  the  pre- liminary  survey  for  this  work  takes  the  form  of a topographic survey. In the final stage, the work may  consist  of  the  following: 1.  Locating  the  center  line,  usually  marked  by stakes at 100-ft intervals called stations 2.  Determining  elevations  along  and  across the   center   line   for   plotting   profile   and   cross sections 3. Plotting the profile and cross sections and fixing the grades 4. Computing the volumes of earthwork and preparing a mass diagram 5. Staking out the extremities for cuts and fills 6. Determining drainage areas to be used in the  design  of  ditches  and  culverts 7. Laying out structures, such as bridges and culverts 8.  Locating  right-of-way  boundaries,  as  well as  staking  out  fence  lines,  if  necessary SPECIAL  SURVEYS As  mentioned  earlier  in  this  chapter, SPECIAL SURVEYS are conducted for a specific purpose  and  with  a  special  type  of  surveying equipment  and  methods.  A  brief  discussion  of some  of  the  special  surveys  familiar  to  you follows. Land Surveys LAND  SURVEYS  (sometimes  called  cadastral or  property  surveys)  are  conducted  to  establish the  exact  location,  boundaries,  or  subdivision  of a tract of land in any specified area. This type of survey  requires  professional  registration  in  all states. Presently, land surveys generally consist of  the  following  chores: 1.  Establishing  markers  or  monuments  to define and thereby preserve the boundaries of land belonging to a private concern, a corporation, or the  government. 2.  Relocating  markers  or  monuments  legally established  by  original  surveys.  This  requires examining previous survey records and retracing what  was  done.  When  some  markers  or  monu- ments are missing, they are reestablished following recognized  procedures,  using  whatever  informa- tion  is  available. 3.  Rerunning  old  land  survey  lines  to  deter- mine their lengths and directions. As a result of the high cost of land, old lines are remeasured to get  more  precise  measurements. 4. Subdividing landed estates into parcels of predetermined sizes and shapes. 5.  Calculating  areas,  distances,  and  directions and  preparing  the  land  map  to  portray  the  survey data so that it can be used as a permanent record. 6.  Writing  a  technical  description  for  deeds. Control Surveys CONTROL   SURVEYS   provide   “basic   con- trol” or horizontal and vertical positions of points to  which  supplementary  surveys  are  adjusted. These types of surveys (sometimes termed  geodetic surveys)   are   conducted   to   provide   geographic positions and plane coordinates of triangulation and traverse stations and the elevations of bench marks. These control points are further used as references  for  hydrographic  surveys  of  the  coastal waters;  for  topographic  control;  and  for  the control of many state, city, and private surveys. 11-3