Topographic surveying; including geographic, exploratory, and military mapping, with hints on camping, emergency surgery, and photography . ened. The control sheet is attached to a plane-table board. Starting from a known section corner, he drivesin a straight line down one of the section lines to other sec-tion corners, determining his position by counting revolutionsof the wheel (Art. 98) and sketching contour crossings as heprogresses. Starting out with a known elevation from spirit-levels(Chap. XV), he determines other elevations as he proceeds bysetting up his plane-table at a section cor
Topographic surveying; including geographic, exploratory, and military mapping, with hints on camping, emergency surgery, and photography . ened. The control sheet is attached to a plane-table board. Starting from a known section corner, he drivesin a straight line down one of the section lines to other sec-tion corners, determining his position by counting revolutionsof the wheel (Art. 98) and sketching contour crossings as heprogresses. Starting out with a known elevation from spirit-levels(Chap. XV), he determines other elevations as he proceeds bysetting up his plane-table at a section corner or opposite ahouse which he can locate by odometer distance, and readsvertical angles from the point of known elevation to houses^windmills, or other objects in sight (Art. 162), drawing direc-tion lines to them as an aid in their identification (Art. 84).Driving on until he comes to one of these objects and beingthus able to locate it on his plane-table, he measures the dis-tance from it to the point from which the angle was taken andat once computes his elevation (Art. 161). Or, setting up his 38 SURVEYING FOR SMALL-SCALE / -10 .^ --20 21 -ol>- S^ 28- 47- — 33- -ij4- FiG. 5.—Land Survey Control for Topographic Sketching. North Dakota. Original scale 2 inches to i mile. SKETCHIiXG OVER PUBLIC LAND LINES. 39 plane-table board from some known position, as determinedfrom his section lines and odometer, he reads vertical angles tohouses or windmills, the heights of which have already beendetermined by vertical angulation, and thus brings down tohis present position an elevation by means of the angle readand distance measured on his board. In conducting verticalangulation in this manner care must be taken to sight at somewell-defined point, as a platform or top of a windmill, thegable or top of a house or top of door-sill, etc. As the sketching is a comparatively simple process underthese conditions because of the flatness of the terrane, hiswork may be expedited
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