Topographic maps and sketch mapping . Fig. 69.—Correction of a Downward Sight. elevation is found by solving the right-angle triangle ABCof Fig. 53 for the side BC. That is, we may lay off the verticalangle BAC to scale and also the horizontal distance, and thenscale off the height BC. Or we may solve this triangle byproper mathematical formula?. A large amount of time andlabor can be saved by using a slope diagram such as that MEASUREMENT OF ELEVATIONS 121 133/ Nl 30NV1SI0 IV0I1U3A. ^ S oc o £ £ £ uj •* a. u. o 122 CONTOUR MAPPING illustrated in Fig. 70, which consists simply of a drawing tos
Topographic maps and sketch mapping . Fig. 69.—Correction of a Downward Sight. elevation is found by solving the right-angle triangle ABCof Fig. 53 for the side BC. That is, we may lay off the verticalangle BAC to scale and also the horizontal distance, and thenscale off the height BC. Or we may solve this triangle byproper mathematical formula?. A large amount of time andlabor can be saved by using a slope diagram such as that MEASUREMENT OF ELEVATIONS 121 133/ Nl 30NV1SI0 IV0I1U3A. ^ S oc o £ £ £ uj •* a. u. o 122 CONTOUR MAPPING illustrated in Fig. 70, which consists simply of a drawing toscale showing a large number of vertical angles and horizontaldistances which enable us to secure graphically the differencein elevation without making a separate drawing for eachproblem. If a horizontal distance, for example, is 500 yds.,and the vertical angle is 3°, the difference in elevation may beread on the right-hand edge of the sheet as about 80 ft. Ifthe distance had been 300 yds. the difference in elevationread in the same way would have been about 48 ft. Dis-tances greater than 500 yds. can be handled by the samediagram by dividing the distance in two or more parts andadding together the vertical distances obtained for each part. EXERCISE Determine the elevation of the different set-up points in the closed traverseused as the exercise in connection with Art. 24. Assume the elevationof the starting point as 100 or any other figure necessary to make allthe eleva
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectcartogr, bookyear1920
