APPENDIX A 



SURVEY METHODS EMPLOYED IN THE CONSTRUCTION OF 

 THE SEVEN ACCOMPANYING TOPOGRAPHIC SHEETS 



By Kai Hendriksen, Topographer 



The main part of the topographical outfit consisted of (1) a 4-inch 

 theodolite, Buff and Buff, the upper part detachable, (2) an 18 x 24 inch 

 plane-table with Johnson tripod and micro-meteralidade. These instru- 

 ments were courteously loaned the expedition by the U. S. Coast and 

 Geodetic Survey and the U. S. Geological Survey respectively. 



The method of survey planned was a combination of graphic triangula- 

 tion and traverse with the micro-meteralidade. All directions were plotted 

 on the plane-table which was oriented by backsight; distances were deter- 

 mined by the micro-meteralidade or triangulation, or both combined; and 

 elevations were obtained by vertical angles. Finally, astronomical observa- 

 tions, usually to the sun, were taken at intervals of about 60 miles for 

 latitude and azimuth to check the triangulation. No observations were 

 made for differences in longitude because this would probably not have 

 given any reliable result, considering the time and instruments at our 

 disposal. Because the survey was to follow very closely the seventy-third 

 meridian west of Greenwich, directions and distances, checked by latitude 

 and azimuth observations, undoubtedly afforded far better means of deter- 

 mining the longitude than time observations. In other words, the time 

 observations made in connection with azimuth observations were not used 

 for computing longitudinal differences. Absolute longitude was taken 

 from existing observations of principal places. 



Principal topographical points were located by from two to four inter- 

 sections from the triangulation and plane-table stations ; and elevations 

 were determined by vertical angle measurements. Whenever practicable, 

 the contours were sketched in the field; the details of the topography 

 otherwise depend upon a great number of photographs taken by Pro- 

 fessor Bowman from critical stations or other points which it was possible 

 to locate on the maps. 



Cross- Section Map from Abancat to CamanI at the Pacific Ocean 



Seven sheets. Scale, 1 : 125,000 ; contour interval, 200 feet. Datum is mean 

 sea level. Astronomical control : 5 latitude and 5 azimuth observations as 

 indicated on the accompanying topographic sheets. 



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