Obtaining Control in Unsurvcyed Toivnships. 377 



points of control upon it and these points are definitely tied in 

 upon neighboring land corners. 



These points will give both vertical and horizontal control if the 

 elevation of the peaks has been determined by vertical angles. 



The Resection Method of Obtaining Main Control in Unsurzfeyed 



Townships. 



The topographer moves his camp into the unsurveyed township 

 to be worked. Under ordinary circumstances he would employ 

 traverse lines entirely for his primary control, extending his 

 traverse lines from the land corners of the surveyed townships. 

 In order to secure vertical control he must carry his elevations 

 by transit line from a B. M. at some distance. Unnecessary transit 

 lines can be eliminated by this method- He sends out his transit 

 crew to establish an initial point for the survey. The field work in 

 establishing this initial point can be performed in a few hours. 

 The vertical control is obtained with the horizontal control. From 

 a convenient strategic commanding point of view the transit 

 man takes three sets of sights upon triangulation points of control 

 already located upon the base plat. The transit plates can be 

 oriented by the compass needle three times, once for each set of 

 angles. The horizontal and vertical angles to triangulation points 

 of control are entered in the note book. 



A hub is established to mark the point and the crew returns to 

 the camp. This work can be performed while the camp is being 

 set up by the other men. In the evening the topographer locates 

 this initial point by resection upon the base plat. He then has 

 three solutions for the elevation of his initial point, and he has two 

 intersections for horizontal location. This gives a sufficient check 

 upon the accuracy of the work. The initial point when plotted 

 upon the base plat now becomes a point of primar}' control, both 

 horizontal and vertical. It can be made a B. M. 



The section lines are projected upon this base plat from the 

 neighboring township by means of fine lines. 



The topographer draws a meridian through his initial point 

 plotted on the base plat. He then scales the distance along this 

 meridianal line to the nearest projected section line and enters 

 that distance in chains or feet on the sheet of instructions to his 

 transit or base line crew. He then scales the distance along the 



